Nucleotide Of Codon Research Articles

Advantages of a Mechanistic Codon Substitution Model for Evolutionary Analysis of Protein-Coding Sequences

BackgroundA mechanistic codon substitution model, in which each codon substitution rate is proportional to the product of a codon mutation rate and the average fixation probability depending on the type of amino acid replacement, has advantages over nucleotide, amino acid, and empirical codon substitution models in evolutionary analysis of protein-coding sequences. It can approximate a wide range of codon substitution processes. If no selection pressure on amino acids is taken into account, it will become equivalent to a nucleotide substitution model. If mutation rates are assumed not to depend on the codon type, then it will become essentially equivalent to an amino acid substitution model. Mutation at the nucleotide level and selection at the amino acid level can be separately evaluated.ResultsThe present scheme for single nucleotide mutations is equivalent to the general time-reversible model, but multiple nucleotide changes in infinitesimal time are allowed. Selective constraints on the respective types of amino acid replacements are tailored to each gene in a linear function of a given estimate of selective constraints. Their good estimates are those calculated by maximizing the respective likelihoods of empirical amino acid or codon substitution frequency matrices. Akaike and Bayesian information criteria indicate that the present model performs far better than the other substitution models for all five phylogenetic trees of highly-divergent to highly-homologous sequences of chloroplast, mitochondrial, and nuclear genes. It is also shown that multiple nucleotide changes in infinitesimal time are significant in long branches, although they may be caused by compensatory substitutions or other mechanisms. The variation of selective constraint over sites fits the datasets significantly better than variable mutation rates, except for 10 slow-evolving nuclear genes of 10 mammals. An critical finding for phylogenetic analysis is that assuming variable mutation rates over sites lead to the overestimation of branch lengths.

The Complete Mitochondrial Genome of the Damsel Bug Alloeorhynchus bakeri (Hemiptera: Nabidae)

The complete sequence of the mitochondrial DNA (mtDNA) of the damsel bug, Alloeorhynchus bakeri, has been completed and annotated in this study. It represents the first sequenced mitochondrial genome of heteropteran family Nabidae. The circular genome is 15, 851 bp in length with an A+T content of 73.5%, contains the typical 37 genes that are arranged in the same order as that of the putative ancestor of hexapods. Nucleotide composition and codon usage are similar to other known heteropteran mitochondrial genomes. All protein-coding genes (PCGs) use standard initiation codons (methionine and isoleucine), except COI, which started with TTG. Canonical TAA and TAG termination codons are found in eight protein-coding genes, the remaining five (COI, COII, COIII, ND5, ND1) have incomplete termination codons (T or TA). PCGs of two strands present opposite CG skew which is also reflected by the nucleotide composition and codon usage. All tRNAs have the typical clover-leaf structure, except the dihydrouridine (DHU) arm of tRNA(Ser (AGN))which forms a simple loop as known in many other metazoa. Secondary structure models of the ribosomal RNA genes of A. bakeri are presented, similar to those proposed for other insect orders. There are six domains and 45 helices and three domains and 27 helices in the secondary structures of rrnL and rrnS, respectively. The major non-coding region (also called control region) between the small ribosomal subunit and the tRNA(Ile )gene includes two special regions. The first region includes four 133 bp tandem repeat units plus a partial copy of the repeat (28 bp of the beginning), and the second region at the end of control region contains 4 potential stem-loop structures. Finally, PCGs sequences were used to perform a phylogenetic study. Both maximum likelihood and Bayesian inference analyses highly support Nabidae as the sister group to Anthocoridae and Miridae.

Complete mitochondrial genome of the laced fritillary Argyreus hyperbius (Lepidoptera: Nymphalidae).

We investigated the complete mitochondrial genome (mitogenome) of Argyreus hyperbius. The 15156 bp long genome harbored the gene content (13 protein coding genes, 22 tRNA genes, 2 rRNA genes and an A+T-rich region) and the gene arrangement was identical to all known lepidopteran mitogenomes. Mitogenome sequence nucleotide organization and codon usage analyses showed that the genome had a strong A+T bias, accounting for A+T content of 80.8%, with a small negative AT skew (-0.019). Eleven intergenic spacers totaling 96 bp, and 14 overlapping regions totaling 34 bp were scattered throughout the whole genome. As has been observed in other lepidopteran species, 12 of the 13 protein-coding genes (PCGs) were initiated by ATN codons, while the COI gene was tentatively designated by the CGA codon. A total of 11 PCGs harbored the complete termination codon TAA, while the COI and COII genes ended at a single T residue. All of the 22 tRNA genes showed typical clover structures except that the tRNA(Ser(AGN)) lacks the dihydrouridine (DHU) stem which is replaced by a simple loop. The intergenic spacer sequence between the tRNA(Ser(AGN)) and ND1 also contained the ATACTAA motif, which is conserved in all other lepidopterans as well. Additionally, the 349 bp A+T-rich region was not comprised of large tandem repetitive sequences, but harbored a few structures common to other lepidopteran insects, such as the motif ATAGA followed by a 20 bp poly-T stretch, a microsatellite-like (AT)(9) element preceded by the ATTTA motif, and a 5 bp poly-A site present immediately upstream of tRNA(Met). The mitochondrial genomic sequence features found in this study not only contribute to genetic diversity information of the group, but also are useful in future studies of the endangered nymphalid butterfly in population genetic dynamics, species conservation, phylogeography and evolution.

Synonymous codon usage bias of spike genes of porcine epidemic diarrhea virus

Synonymous codons are not used randomly. Rather, some codons are used more frequently than others. Investigating codon usage bias is essential to the understanding of viral evolution. However the factors shaping synonymous codon usage bias and nucleotide composition in animal viruses have been studied only to a limited extent. In our study, using the 19 complete CDS sequences of Spike (S) genes of porcine epidemic diarrhea virus (PEDV), we analyzed synonymous codon usage bias. The relative synonymous codon usage (RSCU) was used to estimate codon usage variation in each gene, and the results indicated that preferentially used codons were A-ended, G-ended, and U-ended codons. Effective number of codons (ENC) values varies from 48.15 to 49.52, which suggested that the codon usage bias in PEDV S genes was very slightly. Correspondence analysis (COA) was further performed to study the major trend in codon usage variation, and the plot of ENC values against GC3s (at synonymous third codon position) revealed that mutational pressure rather than translational selection was the main factor determining the codon usage bias in PEDV S genes. Moreover, correlation analysis indicated that aromaticity and hydrophobicity of S genes also influenced the codon usage variation in a minor way. Our study provides the most comprehensive analysis to date of PEDV S genes’ codon usage patterns and provides a basic understanding of the mechanisms for codon usage bias. Key words: Porcine epidemic diarrhea virus, Spike gene, relative synonymous codon usage, effective number of codons, correspondence analysis, correlation analysis.

The characteristic of codon usage pattern and its evolution of hepatitis C virus

To give a new perspective on the codon usage of the hepatitis C virus (HCV) and the factors accounting for shaping the codon usage pattern of the virus, the relative synonymous codon usage (RSCU) values, aromaticity and hydrophobicity of each polyprotein of the virus, effective number of codons (ENC) values and nucleotide contents were calculated to implement a comparative analysis to evaluate the dynamics of the virus evolution. The RSCU values of each codon of 144 HCV ORFs indicated that all abundant codons were C/G-ended codons. The plots of principal component analysis based on sub-genotype of HCV indicated that sub-genotype 1a and 1b separated clearly on the axis of f2 suggesting that the codon usage bias between sub-genotype 1a and 1b strains was different. By comparing the codon usage between HCV and human cells, we found that the synonymous codon usage pattern of HCV was a mixture of coincidence and antagonism to that of host cells. The characteristics of the synonymous codon usage patterns and nucleotide contents of HCV, and the correlation analysis between GC3s, GC1,2s, GC% (ORF), GC% (5′-UTR), GC% (3′-UTR), aromaticity, hydrophobicity and ENC value, respectively, indicated that mutational pressure was the dominant factor accounting for the codon usage variation and selection pressure also accounted for HCV codon usage pattern.

A Comparative Survey of the Frequency and Distribution of Polymorphism in the Genome of Xenopus tropicalis

Naturally occurring DNA sequence variation within a species underlies evolutionary adaptation and can give rise to phenotypic changes that provide novel insight into biological questions. This variation exists in laboratory populations just as in wild populations and, in addition to being a source of useful alleles for genetic studies, can impact efforts to identify induced mutations in sequence-based genetic screens. The Western clawed frog Xenopus tropicalis (X. tropicalis) has been adopted as a model system for studying the genetic control of embryonic development and a variety of other areas of research. Its diploid genome has been extensively sequenced and efforts are underway to isolate mutants by phenotype- and genotype-based approaches. Here, we describe a study of genetic polymorphism in laboratory strains of X. tropicalis. Polymorphism was detected in the coding and non-coding regions of developmental genes distributed widely across the genome. Laboratory strains exhibit unexpectedly high frequencies of genetic polymorphism, with alleles carrying a variety of synonymous and non-synonymous codon substitutions and nucleotide insertions/deletions. Inter-strain comparisons of polymorphism uncover a high proportion of shared alleles between Nigerian and Ivory Coast strains, in spite of their distinct geographical origins. These observations will likely influence the design of future sequence-based mutation screens, particularly those using DNA mismatch-based detection methods which can be disrupted by the presence of naturally occurring sequence variants. The existence of a significant reservoir of alleles also suggests that existing laboratory stocks may be a useful source of novel alleles for mapping and functional studies.

Analysis of horizontal transfer gene of <I>Bombyx mori</I> NPV

For research on genetic characters and evolutionary origin of the genome of baculoviruses, a comprehensive homology search and phylogenetic analysis of the complete genomes of Bombyx mori NPV and Bombyx mori were used. Three horizontally transferred genes (inhibitor of apoptosis, chitinase, and UDP-glucosyltransferase) were identified, and there was evidence that all of these genes were derived from the insect host. The results of analysis showed lots of differences between the features of horizontal transferred genes and the ones of whole genomic genes, such as nucleotide composition, codon usagebias and selection pressure. These results reconfirmed that the horizontally transferred genes are exogenous. The analysis of gene function suggested that horizontally transferred genes acquired from an ancestral host insect can increase the efficiency of baculoviruses transmission.

Analysis of synonymous codon usage bias, nucleotide and amino acid composition in 13 species of Flaviviridae

Flaviviridae are viruses that cause several diseases including Dengue fever, Japanese encephalitis, Murray Valley encephalitis, Tick-borne encephalitis, West Nile encephalitis, Yellow fever and Hepatitis C Virus Infection. Members of this family have monopartite, linear, single-stranded RNA genomes of positive polarity, 9.6-12.3 kb in length. Here, we have analyzed the codon usage of 13 species of this family by using gene infinity pakage. Base and amino acid composition analysis was also performed by CAIcal server and PseAAC web-sever respectively. The results showed that the highest number of A, G and C bases were seen in the RNA genome of Dengue virus 2, Tick borne encephalitis virus and Hepatitis C virus respectively. Although the number of U base used in RNA genomes was very close, the highest U nucleotide amount was 23.77% in Wesselsbron virus. The lowest number of C, G, U and A bases was seen in Bovine viral diarrhea virus, Dengue virus 2, Tick borne encephalitis virus and Hepatitis C virus respectively. In this study, it is found that the complete genome of classical swine fever virus has a lower GC content and genome of Tick borne encephalitis virus, Hepatitis C virus and Powassan virus have a higher GC content than other species. We also classified the amino acids as rare (Phenylalanine, Cysteine, Histidine, Methionine, Asparagine, Glutamine, Tryptophan and Tyrosine), frequent (Alanine, Glutamic acid, Glycine, Leucine, Valine and Threonine), and intermediate (all others). The highest and the lowest number of preferred codons exist in Wesselsbron virus and West Nile virus, respectively.

Viral SELEX reveals individual and cooperative roles of the C-box and G-box in HIV-2 replication

The 5' UTR of HIV-2 genomic RNA contains signaling motifs that regulate specific steps of the replication cycle. Two motifs of interest are the C-box and the G-box. The C-box is found in the 5' untranslated region upstream of the primer binding site, while the G-box is found downstream from the major splice donor site, encompassing the gag start codon and flanking nucleotides. Together the C-box and the G-box form a long-range base-pairing interaction called the CGI. We and others have previously shown that formation of the CGI affects RNA dimerization in vitro and the positions of the C-box and the G-box are suggestive of potential roles of the CGI in other steps of HIV-2 replication. Therefore, we attempted to elucidate the role of the CGI using a viral SELEX approach. We constructed proviral DNA libraries containing randomized regions of the C-box or G-box paired with wild-type or mutant base-pairing partners. These proviral DNA libraries were transfected into COS-7 cells to produce viral libraries that were then used to infect permissive C8166 cells. The "winner" viruses were sequenced and further characterized. Our results demonstrate that there is strong selective pressure favoring viruses that can form a branched CGI. In addition, we show that the mutation of the C-box alone can enhance RNA encapsidation, and mutation of the G-box can alter the levels of Gag protein isoforms. These results suggest coordinated regulation of RNA translation, dimerization, and encapsidation during HIV-2 replication.

Both swine and human cells are capable to support the replication of swine hepatitis E virus type 4 in vitro

Using swine anal swab or liver as inocula, cell-culture systems were developed for swine hepatitis E virus (HEV) in swine cells (IBRS-2) and human cells (A549). Both positive and negative strand of swine HEV RNA were detected continuously. Cytopathic effect appeared from passage 8 in IBRS-2 and passage 22 in A549. Viral antigen was detected by indirect immunofluorescent assay in infected cells. Progenies harbored mutations in the third nucleotide of codon. Amino acid changes occurred in passage 8 in IBRS-2 and rescued in passage 10. Full-length genome sequence of a swine HEV isolate from liver was determined to be genotype 4. Taken together, our data suggest that swine HEV is able to replicate in both swine and human cells in vitro.

Analysis of codon usage and nucleotide composition bias in polioviruses

BackgroundPoliovirus, the causative agent of poliomyelitis, is a human enterovirus and a member of the family of Picornaviridae and among the most rapidly evolving viruses known. Analysis of codon usage can reveal much about the molecular evolution of the viruses. However, little information about synonymous codon usage pattern of polioviruses genome has been acquired to date.MethodsThe relative synonymous codon usage (RSCU) values, effective number of codon (ENC) values, nucleotide contents and dinucleotides were investigated and a comparative analysis of codon usage pattern for open reading frames (ORFs) among 48 polioviruses isolates including 31 of genotype 1, 13 of genotype 2 and 4 of genotype 3.ResultsThe result shows that the overall extent of codon usage bias in poliovirus samples is low (mean ENC = 53.754 > 40). The general correlation between base composition and codon usage bias suggests that mutational pressure rather than natural selection is the main factor that determines the codon usage bias in those polioviruses. Depending on the RSCU data, it was found that there was a significant variation in bias of codon usage among three genotypes. Geographic factor also has some effect on the codon usage pattern (exists in the genotype-1 of polioviruses). No significant effect in gene length or vaccine derived polioviruses (DVPVs), wild viruses and live attenuated virus was observed on the variations of synonymous codon usage in the virus genes. The relative abundance of dinucleotide (CpG) in the ORFs of polioviruses are far below expected values especially in DVPVs and attenuated virus of polioviruses genotype 1.ConclusionThe information from this study may not only have theoretical value in understanding poliovirus evolution, especially for DVPVs genotype 1, but also have potential value for the development of poliovirus vaccines.

The characteristics of the synonymous codon usage in enterovirus 71 virus and the effects of host on the virus in codon usage pattern

To give a new perspective on the evolutionary characteristics shaping the genetic diversity of enterovirus 71 (EV71) and the effects of natural selection from its host on the codon usage pattern of the virus, the relative synonymous codon usage (RSCU) values, codon usage bias (CUB) values, effective number of codons (ENCs) values and nucleotide contents were calculated to implement a comparative analysis to evaluate the dynamics of the virus evolution. The characteristics of the synonymous codon usage patterns and nucleotide contents of EV71 and the comparison between ENC values for the whole coding sequence of EV71 and that of coding sequences for viral proteins of EV71 all indicate that the interaction between mutation pressure from virus and natural selection from host exists in the processes of evolution of EV71. The synonymous codon usage pattern of EV71 is a mixture of coincidence and antagonism to that of host cell. In addition, the genetic diversity of EV71 strains and the preferential selection of some synonymous codons in EV71 strains based on the different epidemic areas were observed, suggesting that geographic and social factors may play roles in influencing the evolution of this virus.

Study of genetic heterogeneity of hemoglobinopathy and β-thalassemia molecular variants in newborns

A complex of molecular-genetic and biochemical methods, such as hemoglobin isoelectric focusing and the amplification of refractory mutation systems, have been used for the first time to screen for inherited hemoglobinopathies among newborns in Baku. The phenotypical frequencies of pathological genes of α- and β-thalassemias and abnormal hemoglobins S and D were 2.48, 1.95, 0.35, and 0.09%, respectively. Three types of mutations at β-thalassemia were identified, including the deletion of two nucleotides (two adenines) in codon 8 of the first exon (36.2%), the substitution of the guanine nucleotide for the adenine nucleotide at position 110 of intron-1, and the substitution of guanine nucleotide for adenine nucleotide at position 1 of intron-2 (13.79%) in the β-hemoglobin gene.

Complete mitochondrial genome sequences of three Crocodylus species and their comparison within the Order Crocodylia

Crocodylus is the largest genus within the Order Crocodylia consisting of eleven species. This paper reports the complete mitochondrial genome sequences of three Crocodylus species, Crocodylus moreletii, Crocodylus johnstoni and Crocodylus palustris, and compares the newly obtained mitochondrial DNA sequences with other crocodilians, available in the public databases. The mitochondrial genomes of C. moreletii, C. johnstoni and C. palustris are 16,827 bp, 16,851 bp and 16,852 bp in length, respectively. These mitochondrial genomes consist of 13 protein coding genes, two ribosomal RNA genes, 22 transfer RNA genes and a non-coding region. The mitochondrial genomes of all the Crocodylus species, studied herein show identical characteristics in terms of nucleotide composition and codon usage, suggestive of the existence of analogous evolutionary patterns within the genus, Crocodylus. The synonymous and non-synonymous substitution rates for all the protein coding genes of Crocodylus were observed in between 0.001 and 0.275 which reveal the prevalence of purifying selection in these genes. The phylogenetic analyses based on complete mitochondrial DNA data substantiate the previously established crocodilian phylogeny. This study provides a better understanding of the crocodilian mitochondrial genome and the data described herein will prove useful for future studies concerning crocodilian mitochondrial genome evolution.

Analysis of codon usage in Newcastle disease virus

In this study, the relative synonymous codon usage (RSCU) values, effective number of codon (ENC) values, nucleotide contents, and dinucleotide were used to investigate codon usage pattern of each protein-coding gene and genome among 31 Newcastle disease virus (NDV) isolates. The result shows that the overall extent of codon usage bias in NDV is low (mean ENC = 56.15 > 40). The good correlation between the (C + G)12% and (G + C)3% suggests that the mutational pressure, rather than natural selection, is the main factor that determines the codon usage bias and base component in NDV. It is observed that synonymous codon usage pattern in NDV genes is gene function and geography specific, but not host specific. By contrasting synonymous codon usage patterns of different NDV isolates, we suggest that more than one genotype of NDV circulates in waterfowl in USA; and gene length has no significant effect on the variations of synonymous codon usage in these virus genes. CpG under-represented is a characteristic for NDV to fit in its host. These results not only provide an insight into the variation of codon usage pattern among the genomes of NDV, but also may help in understanding the processes governing the evolution of NDV.Electronic supplementary materialThe online version of this article (doi:10.1007/s11262-011-0574-z) contains supplementary material, which is available to authorized users.

Analysis of human P[4]G2 rotavirus strains isolated in Brazil reveals codon usage bias and strong compositional constraints

The Rotavirus genus belongs to the family Reoviridae and its genome consist of 11 segments of double-stranded RNA. Group A rotaviruses (RV-A) are the main etiological agent of acute viral gastroenteritis in infants and young children worldwide. Understanding the extent and causes of biases in codon usage is essential to the understanding of viral evolution. However, the factors shaping synonymous codon usage bias and nucleotide composition in human RV-A are currently unknown. In order to gain insight into these matters, we analyzed the codon usage and base composition constraints on the two genes that codify the two outer capsid proteins (VP4 [VP8*] and VP7) of 58 P[4]G2 RV-A strains isolated in Brazil and investigated the possible key evolutionary determinants of codon usage bias. The results of these studies revealed that the frequencies of codon usage in both RV-A proteins studied are significantly different than the ones used by human cells. In order to observe if similar trends of codon usage are found when RV-A complete genomes are considered, we compare these results with results found using a dataset of 10 reference strains for whom the complete codes of the 11 segments are known. Similar results were obtained using capsid proteins or complete genomes. The general correlations found between the position of each sequence on the first axis generated by correspondence analysis and the relative dinucleotide abundances indicate that codon usage in RV-A can also be strongly influenced by underlying biases in dinucleotide frequencies. CpG and GpC containing codons are markedly suppressed. Thus, the results of this study suggest that RV-A genomic biases are the result of the evolution of genome composition in relation to host adaptation and the ability to escape antiviral cell responses.

Genus specific evolution of codon usage and nucleotide compositional traits of poxviruses.

Poxviruses are complex in their nucleotide compositional features of the coding regions. The codon usages in Poxviruses are in accordance with their compositional bias. In the Poxviridae family, codon usage patterns and nucleotide compositional traits are widely divergent across species but some conservation was observed within a genus. Viruses from six Chordopox genera, i.e., Avipoxvirus, Capripoxvirus, Cervidpoxvirus, Orthopoxvirus, Suipoxvirus, Yatapoxvirus, and one Entomopox genus- Betaentomopoxvirus, and some unclassified Entomopoxvirus are significantly rich in AT composition. Four other Chordopox genera- Molluscipoxvirus, Orthopoxvirus, Parapoxvirus, and some unclassified Chordopoxvirus are dominated by the GC rich viruses. Poxviruses from these AT rich and GC rich genera preferred AT or GC ending codons owing to their respective nucleotide compositional bias. For example, viruses from AT rich Orthopoxvirus, or GC rich Parapoxvirus have evolved with mutually exclusive type codon preferences following their genus-specific nucleotide compositions. Additional factors like gene length and expression level also influenced their codon usage patterns to some extent in some Poxvirus genera. Evidences from correspondence analysis and cluster analysis on the extent of divergence in codon usage also support this genus specific evolution of Poxvirus codon usage. Analyzes suggest that most of the Poxviruses from different genera, have evolved in almost two different evolutionary trajectory in context of their nucleotide composition and codon usage.

Analysis of codon usage in bovine viral diarrhea virus

Bovine viral diarrhea virus (BVDV) is a widespread virus in beef and dairy herds. BVDV has been grouped into two genotypes, genotype 1 and genotype 2. In this study, the relative synonymous codon usage (RSCU) values, effective number of codon (ENC) values and nucleotide content were investigated, and a comparative analysis of codon usage patterns for open reading frames (ORFs) of 22 BVDV genomes, including 14 of genotype 1 and 8 of genotype 2, was carried out. A high A+U content and low codon bias were found in BVDV genomes. Depending on the RSCU data, it was found that there was a significant variation in bias of codon usage between the two genotypes, and a geographic factor exists only in genotype-1 of BVDV. The RSCU data have a negative correlation with general average hydrophobicity (GRAVY), aromaticity and nucleotide content. Furthermore, the overall abundance of C and U has no effect on the synonymous codon usage patterns. In contrast, the A and G content showed a significant correlation with the nucleotide content at the third position. In addition, the codon usage patterns of BVDV are similar to those of 22 conserved genes of Bos taurus. Taken together, the genetic characteristics of BVDV possibly result from interactions between natural seclection and mutation pressure.Electronic supplementary materialThe online version of this article (doi:10.1007/s00705-010-0848-0) contains supplementary material, which is available to authorized users.

Localizing triplet periodicity in DNA and cDNA sequences

BackgroundThe protein-coding regions (coding exons) of a DNA sequence exhibit a triplet periodicity (TP) due to fact that coding exons contain a series of three nucleotide codons that encode specific amino acid residues. Such periodicity is usually not observed in introns and intergenic regions. If a DNA sequence is divided into small segments and a Fourier Transform is applied on each segment, a strong peak at frequency 1/3 is typically observed in the Fourier spectrum of coding segments, but not in non-coding regions. This property has been used in identifying the locations of protein-coding genes in unannotated sequence. The method is fast and requires no training. However, the need to compute the Fourier Transform across a segment (window) of arbitrary size affects the accuracy with which one can localize TP boundaries. Here, we report a technique that provides higher-resolution identification of these boundaries, and use the technique to explore the biological correlates of TP regions in the genome of the model organism C. elegans.ResultsUsing both simulated TP signals and the real C. elegans sequence F56F11 as an example, we demonstrate that, (1) Modified Wavelet Transform (MWT) can better define the boundary of TP region than the conventional Short Time Fourier Transform (STFT); (2) The scale parameter (a) of MWT determines the precision of TP boundary localization: bigger values of a give sharper TP boundaries but result in a lower signal to noise ratio; (3) RNA splicing sites have weaker TP signals than coding region; (4) TP signals in coding region can be destroyed or recovered by frame-shift mutations; (5) 6 bp periodicities in introns and intergenic region can generate false positive signals and it can be removed with 6 bp MWT.ConclusionsMWT can provide more precise TP boundaries than STFT and the boundaries can be further refined by bigger scale MWT. Subtraction of 6 bp periodicity signals reduces the number of false positives. Experimentally-introduced frame-shift mutations help recover TP signal that have been lost by possible ancient frame-shifts. More importantly, TP signal has the potential to be used to detect the splice junctions in fully spliced mRNA sequence.

Influence of codon usage bias on FGLamide-allatostatin mRNA secondary structure

The FGLamide allatostatins (ASTs) are invertebrate neuropeptides which inhibit juvenile hormone biosynthesis in Dictyoptera and related orders. They also show myomodulatory activity. FGLamide AST nucleotide frequencies and codon bias were investigated with respect to possible effects on mRNA secondary structure. 367 putative FGLamide ASTs and their potential endoproteolytic cleavage sites were identified from 40 species of crustaceans, chelicerates and insects. Among these, 55% comprised only 11 amino acids. An FGLamide AST consensus was identified to be (X) 1→16Y(S/A/N/G)FGLGKR, with a strong bias for the codons UUU encoding for Phe and AAA for Lys, which can form strong Watson–Crick pairing in all peptides analyzed. The physical distance between these codons favor a loop structure from Ser/Ala-Phe to Lys-Arg. Other loop and hairpin loops were also inferred from the codon frequencies in the N-terminal motif, and the first amino acids from the C-terminal motif, or the dibasic potential endoproteolytic cleavage site. Our results indicate that nucleotide frequencies and codon usage bias in FGLamide ASTs tend to favor mRNA folds in the codon sequence in the C-terminal active peptide core and at the dibasic potential endoproteolytic cleavage site.