Eukaryotic Regions Research Articles

Identification of exon regions in eukaryotes using fine-tuned variational mode decomposition based on kurtosis and short-time discrete Fourier transform

In genomic research, identifying the exon regions in eukaryotes is the most cumbersome task. This article introduces a new promising model-independent method based on short-time discrete Fourier transform (ST-DFT) and fine-tuned variational mode decomposition (FTVMD) for identifying exon regions. The proposed method uses the N/3 periodicity property of the eukaryotic genes to detect the exon regions using the ST-DFT. However, background noise is present in the spectrum of ST-DFT since the sliding rectangular window produces spectral leakage. To overcome this, FTVMD is proposed in this work. VMD is more resilient to noise and sampling errors than other decomposition techniques because it utilizes the generalization of the Wiener filter into several adaptive bands. The performance of VMD is affected due to the improper selection of the penalty factor (α), and the number of modes (K). Therefore, in fine-tuned VMD, the parameters of VMD (K and α) are optimized by maximum kurtosis value. The main objective of this article is to enhance the accuracy in the identification of exon regions in a DNA sequence. At last, a comparative study demonstrates that the proposed technique is superior to its counterparts.

A High Frequency of Chromosomal Duplications in Unicellular Algae Is Compensated by Translational Regulation.

Although duplications have long been recognized as a fundamental process driving major evolutionary innovations, direct estimates of spontaneous chromosome duplication rates, leading to aneuploid karyotypes, are scarce. Here, from mutation accumulation (MA) experiments, we provide the first estimates of spontaneous chromosome duplication rates in six unicellular eukaryotic species, which range from 1 × 10-4 to 1 × 10-3 per genome per generation. Although this is ∼5 to ∼60 times less frequent than spontaneous point mutations per genome, chromosome duplication events can affect 1-7% of the total genome size. In duplicated chromosomes, mRNA levels reflected gene copy numbers, but the level of translation estimated by polysome profiling revealed that dosage compensation must be occurring. In particular, one duplicated chromosome showed a 2.1-fold increase of mRNA but translation rates were decreased to 0.7-fold. Altogether, our results support previous observations of chromosome-dependent dosage compensation effects, providing evidence that compensation occurs during translation. We hypothesize that an unknown posttranscriptional mechanism modulates the translation of hundreds of transcripts from genes located on duplicated regions in eukaryotes.

Interrelationship amongst varieties of edible mushroom through Molecular marker Study

The information regarding the DNA sequences of plant is very limited. When knowledge of the DNA sequence of the targeted genome is unavailable several PCR based techniques (RAPD, ITS, AFLP, SSR markers, SNP markers) are utilized to accumulate information about the genetic adaptability. Random Amplification of Polymorphic DNA is a technique by which the random segments of DNA are amplified. Short nucleotide primers (8–12 nucleotides) are used to proceed with the PCR using genomic DNA, for fragments to amplify. The primers bind somewhere in the sequence. By comparing the banding matrix the DNA patterns can be ascertained. RAPD has been utilized to characterize, trace the phylogeny of diverse plant species. Internal transcribed spacer (ITS) is to a non-functional RNA situated between structural ribosomal RNAs (rRNA) on a transcript. The sequence of rRNA precursor transcript is the 5' external transcribed sequence (5' ETS), 18S rRNA, ITS1, 5.8S rRNA, ITS2, 28S rRNA and the 3'ETS read from 5' to 3' direction. The complete sequence repeats themselves in tandem array for thousands of copies separated by regions of non-transcribed DNA termed non-transcribed spacer (NTS) or intergenic spacer (IGS). There is the presence of two ITS regions in eukaryotes. The first one located between 18S and 5.8S rRNA genes is called ITS1, while the next in the sequence is ITS2 that lies between 5.8S and 26S rRNA genes in plants. Each eukaryotic ribosomal cluster follows the sequence of the 5' external transcribed sequence (5' ETS), trailed by the 18S rRNA gene, the ITS1 and the 5.8S rRNA gene, the ITS2, the 28S rRNA gene, and finally the 3' ETS. ETS and ITS pieces are excised and rapidly degraded during rRNA maturation. In our study four different gilled mushrooms were analyzed for RAPD and ITS study.

Improved filtering approach for identification of protein-coding regions in eukaryotes by background noise reduction using S–G filter

Unlike prokaryotic genomes, the arrangement of protein-coding regions in eukaryotic genomes is not continuous. It is interrupted by the non-coding DNA sequences called introns. Therefore, the identification of protein-coding regions in a eukaryotic DNA sequence is one of the challenging research issues in bioinformatics. Signal processing-based computational tools such as short-time discreet Fourier transforms (STDFT) and narrow bandpass digital filters has been successfully used to resolve this problem. Filtering techniques are popularly used because of its faster response than the transform techniques. However, the prediction accuracy of the filtering approach is still limited due to background noise present in its spectrum. Background noise masks the discriminative three base periodicity (TBP) features and increases the chances of false prediction. Several de-noising techniques have been proposed so far. Recently, second-order moving average filter has been used to diminish the effect of background noise. However, the problem with moving average filter is that it operates similarly on coding and non-coding regions, and therefore, along with noise reduction, it also affects the spectral features of protein-coding regions which lead to inaccurate prediction results. In this work, we used the Savitzky–Golay (SG) filter for background noise reduction and compared the performance with other existing de-noising techniques. S–G filter works on the local least-squares polynomial approximation principal and act as a weighted moving average filter. This investigation shows that along with noise reduction, S–G filter can preserve the spectral values of coding regions with a greater extent, and therefore, provide more accurate prediction results than other de-noising techniques.

Identification, genetic variation, and structural analysis of 18S rRNA of Theileria orientalis and Theileria velifera-like isolates from Myanmar.

Ribosomal RNA genes have been widely used for the identification and phylogenetic analysis of various organisms, including parasitic protozoa. Here, we report nine near full-length Theileria orientalis 18S rRNA gene sequences from cattle from different areas of Myanmar. Phylogenetic analysis of the 18S rRNA genes revealed a considerably close genetic relationship among T. orientalis isolates from Australia, China, Japan, Korea, Myanmar, and Pakistan. We also obtained four Theileria velifera-like (Theileria cf. velifera) 18S rRNA gene sequences from two cattle and two water buffaloes from the northernmost area of Myanmar. The phylogenetic analysis of T. cf. velifera isolates from Myanmar along with T. velifera and T. cf. velifera isolates from African countries suggested an evolutionary lineage of greater complexity in T. velifera-related parasites. DNA alignment analysis indicated the presence of 51 and 55 nucleotide variation positions within the 18S rRNA genes from 15T. orientalis and 11T. velifera-related isolates, respectively. Alignment entropy analysis of the 18S rRNA sequences indicated that both T. orientalis and T. velifera-related isolates had three hyper variable regions, corresponding to V2, V4, and V7 regions in eukaryotes. The degree of variation was prominent in the V2 in T. orientalis and V4 in T. velifera-related isolates. The secondary structure analysis of the 18S rRNA predicted using minimum free energy algorism revealed that the structure of V4 region differed most significantly between T. orientalis and T. velifera. These results provide novel insights into common structures, variations and functions of small subunit rRNA in Theileria species.

Walsh code based numerical mapping method for the identification of protein coding regions in eukaryotes

The protein coding regions play a significant role for gene applications in genomic signal processing. Unlike prokaryotes, the coding regions in eukaryotes are arranged in a random manner. Owing to unequal lengths and low volume density of coding regions, the identification of coding regions makes cumbersome. In this work, a new numerical mapping method based on Walsh codes is proposed to detect the coding regions in eukaryotes. The Walsh code for each nucleotide is obtained using the statistical features of a DNA sequence. The proposed method uses static type of mapping to convert a string of DNA nucleotides into a numerical sequence. The numerical sequence is given as an input to the digital signal processing based spectrum identification tool to detect the existence of quasi-periodic components within the coding region. The advantage of our method is that it is simple to design and easy to represent. The performance of the proposed method has been tested on four benchmark databases and a random set of sequences collected from the National Center for Biological Information (NCBI) database. Furthermore, it has been compared with other state-of-the-art spectrum based numerical mapping methods for statistical features such as sensitivity, specificity and accuracy. The proposed method is efficient as it attains 94 % accuracy, 85 % sensitivity and 96 % specificity when tested on the benchmark C. Elegans gene sequence.

Genes encoding intrinsic disorder in Eukaryota have high GC content.

We analyze a correlation between the GC content in genes of 12 eukaryotic species and the level of intrinsic disorder in their corresponding proteins. Comprehensive computational analysis has revealed that the disordered regions in eukaryotes are encoded by the GC-enriched gene regions and that this enrichment is correlated with the amount of disorder and is present across proteins and species characterized by varying amounts of disorder. The GC enrichment is a result of higher rate of amino acid coded by GC-rich codons in the disordered regions. Individual amino acids have the same GC-content profile between different species. Eukaryotic proteins with the disordered regions encoded by the GC-enriched gene segments carry out important biological functions including interactions with RNAs, DNAs, nucleotides, binding of calcium and metal ions, are involved in transcription, transport, cell division and certain signaling pathways, and are localized primarily in nucleus, cytosol and cytoplasm. We also investigate a possible relationship between GC content, intrinsic disorder and protein evolution. Analysis of a devised "age" of amino acids, their disorder-promoting capacity and the GC-enrichment of their codons suggests that the early amino acids are mostly disorder-promoting and their codons are GC-rich while most of late amino acids are mostly order-promoting.

Heterochromatin and genome size inDrosophila

Heterochromatin and genome size in<i>Drosophila</i>

Universally increased mRNA stability downstream of the translation initiation site in eukaryotes and prokaryotes

Local secondary structures in coding sequences have important functions across various translational processes. To date, however, the local structures and their functions in the early stage of translation elongation remain poorly understood. Here, we surveyed the structural stability in the first 180 nucleotides of the coding sequence of 27 species using computational method. We found that the structural stability in the 30–80 nucleotide interval was significantly higher than that in other regions in eukaryotes and most prokaryotes. No significant correlation between local translation efficiency and structural stability was observed, suggesting that this structural region has undergone selection pressure directly to maintain high stability. Furthermore, ribosome was blocked by this region, providing an opportunity for co-translational regulation. Remarkably, in eukaryotes, we found that mRNAs with higher structural stability in the 30–80 nucleotide interval tended to encode the secreted proteins. Overall, our results revealed a previously unappreciated correlation between structural stability and protein localization.

Characterization and evolution of 5′ and 3′ untranslated regions in eukaryotes

Untranslated regions (UTRs) in eukaryotes play a significant role in the regulation of translation and mRNA half-life, as well as interacting with specific RNA-binding proteins. However, UTRs receive less attention than more crucial elements such as genes, and the basic structural and evolutionary characteristics of UTRs of different species, and the relationship between these UTRs and the genome size and species gene number is not well understood. To address these questions, we performed a comparative analysis of 5′ and 3′ untranslated regions of different species by analyzing the basic characteristics of 244,976 UTRs from three eukaryote kingdoms (Plantae, Fungi, and Protista). The results showed that the UTR lengths and SSR frequencies in UTRs increased significantly with increasing species gene number while the length and G+C content in 5′ UTRs and different types of repetitive sequences in 3′ UTRs increased with the increase of genome size. We also found that the sequence length of 5′ UTRs was significantly positively correlated with the presence of transposons and SSRs while the sequence length of 3′ UTRs was significantly positively correlated with the presence of tandem repeat sequences. These results suggested that evolution of species complexity from lower organisms to higher organisms is accompanied by an increase in the regulatory complexity of UTRs, mediated by increasing UTR length, increasing G+C content of 5′ UTRs, and insertion and expansion of repetitive sequences.

Distribution of 45S rDNA sites in chromosomes of plants: Structural and evolutionary implications

Background45S rDNA sites are the most widely documented chromosomal regions in eukaryotes. The analysis of the distribution of these sites along the chromosome in several genera has suggested some bias in their distribution. In order to evaluate if these loci are in fact non-randomly distributed and what is the influence of some chromosomal and karyotypic features on the distribution of these sites, a database was built with the position and number of 45S rDNA sites obtained by FISH together with other karyotypic data from 846 plant species.ResultsIn angiosperms the most frequent numbers of sites per diploid karyotype were two and four, suggesting that in spite of the wide dispersion capacity of these sequences the number of rDNA sites tends to be restricted. The sites showed a preferential distribution on the short arms, mainly in the terminal regions. Curiously, these sites were frequently found on the short arms of acrocentric chromosomes where they usually occupy the whole arm. The trend to occupy the terminal region is especially evident in holokinetic chromosomes, where all of them were terminally located. In polyploids there is a trend towards reduction in the number of sites per monoploid complement. In gymnosperms, however, the distribution of rDNA sites varied strongly among the sampled families.ConclusionsThe location of 45S rDNA sites do not vary randomly, occurring preferentially on the short arm and in the terminal region of chromosomes in angiosperms. The meaning of this preferential location is not known, but some hypotheses are considered and the observed trends are discussed.

Organization and Evolution of Subtelomeric Satellite Repeats in the Potato Genome

Subtelomeric domains immediately adjacent to telomeres represent one of the most dynamic and rapidly evolving regions in eukaryotic genomes. A common feature associated with subtelomeric regions in different eukaryotes is the presence of long arrays of tandemly repeated satellite sequences. However, studies on molecular organization and evolution of subtelomeric repeats are rare. We isolated two subtelomeric repeats, CL14 and CL34, from potato (Solanum tuberosum). The CL14 and CL34 repeats are organized as independent long arrays, up to 1-3 Mb, of 182 bp and 339 bp monomers, respectively. The CL14 and CL34 repeat arrays are directly connected with the telomeric repeats at some chromosomal ends. The CL14 repeat was detected at the subtelomeric regions among highly diverged Solanum species, including tomato (Solanum lycopersicum). In contrast, CL34 was only found in potato and its closely related species. Interestingly, the CL34 repeat array was always proximal to the telomeres when both CL14 and CL34 were found at the same chromosomal end. In addition, the CL34 repeat family showed more sequence variability among monomers compared with the CL14 repeat family. We conclude that the CL34 repeat family emerged recently from the subtelomeric regions of potato chromosomes and is rapidly evolving. These results provide further evidence that subtelomeric domains are among the most dynamic regions in eukaryotic genomes.

Inferring an organism-specific optimal threshold for predicting protein coding regions in eukaryotes based on a bootstrapping algorithm

The accuracy of prediction methods based on power spectrum analysis depends on the threshold that is used to discriminate between protein coding and non-coding sequences in the genomes of eukaryotes. Because the structure of genes vary among different eukaryotes, it is difficult to determine the best prediction threshold for a eukaryote relying only on prior biological knowledge. To improve the accuracy of prediction methods based on power spectral analysis, we developed a novel method based on a bootstrap algorithm to infer organism-specific optimal thresholds for eukaryotes. As prior information, our method requires the input of only a few annotated protein coding regions from the organism being studied. Our results show that using the calculated optimal thresholds for our test datasets, the average prediction accuracy of our method is 81%, an increase of 19% over that obtained using the same empirical threshold P=4 for all datasets. The proposed method is simple and convenient and easily applied to infer optimal thresholds that can be used to predict coding regions in the genomes of most organisms.

A new plasmid vector for DNA delivery using lactococci

BackgroundThe use of food-grade lactococci as bacterial carriers to DNA delivery into epithelial cells is a new strategy to develop live oral DNA vaccine. Our goal was to develop a new plasmid, named pValac, for antigen delivery for use in lactococci. The pValac plasmid was constructed by the fusion of: i) a eukaryotic region, allowing the cloning of an antigen of interest under the control of the pCMV eukaryotic promoter to be expressed by a host cell and ii) a prokaryotic region allowing replication and selection of bacteria. In order to evaluate pValac functionality, the gfp ORF was cloned into pValac (pValac:gfp) and was analysed by transfection in PK15 cells. The applicability of pValac was demonstrated by invasiveness assays of Lactococcus lactis inlA+ strains harbouring pValac:gfp into Caco-2 cells.ResultsAfter transfection with pValac:gfp, we observed GFP expression in PK15 cells. L. lactis inlA+ were able to invade Caco-2 cells and delivered a functional expression cassette (pCMV:gfp) into epithelial cells.ConclusionWe showed the potential of an invasive L. lactis harbouring pValac to DNA delivery and subsequent triggering DNA expression by epithelial cells. Further work will be to examine whether these strains are able to deliver DNA in intestinal cells in vivo.

Epigenetics of specific chromosome regions

Investigation of protein complexes, various types of protein modifications and the structure of the chromatin of specific chromosome regions, such as centromeres, telomeres, and adjacent heterochromatic regions, considerably complicated the notion on DNA, prevailing five decades ago, as molecules that exclusively control coding and realization of genetic information. Striking plasticity of the primary structure of centromeric and telomeric DNA suggests a variety of molecular mechanisms underlying fundamental and universal functions of these key chromosome regions. The present review is an attempt to consider the current concepts on the structure of the DNA and protein components, as well as the structure of the chromatin of specific chromosome regions in eukaryotes, and the concerted evolution of these components, leading to the formation of a hierarchy of coordinated DNA-protein complexes.

CUTting genetic noise by polyadenylation-induced RNA degradation

Silencing of genomic regions in eukaryotes is thought to be the result of transcriptional repression. Recent results show that nuclear RNA degradation plays a major role in discarding RNA molecules with no obvious roles that are produced by cryptic RNA polymerase II transcription throughout the Saccharomyces cerevisiae genome. These cryptic transcripts are polyadenylated at their 3'-end by a poly(A) polymerase complex distinct from that used by the mRNA factory, which serves to tag these aberrant transcripts for nuclear degradation.

Genome-wide selection of unique and valid oligonucleotides

Functional genomics methods are used to investigate the huge amount of information contained in genomes. Numerous experimental methods rely on the use of oligo- or polynucleotides. Nucleotide strand hybridization forms the underlying principle for these methods. For all these techniques, the probes should be unique for analyzed genes. In addition to being unique for the studied genes, the probes should fulfill a large number of criteria to be usable and valid. The criteria include for example, avoidance of self-annealing, suitable melting temperature and nucleotide composition. We developed a method for searching unique and valid oligonucleotides or probes for genes so that there is not even a similar (approximate) occurrence in any other location of the whole genome. By using probe size 25, we analyzed 17 complete genomes representing a wide range of both prokaryotic and eukaryotic organisms. More than 92% of all the genes in the investigated genomes contained valid oligonucleotides. Extensive statistical tests were performed to characterize the properties of unique and valid oligonucleotides. Unique and valid oligonucleotides were relatively evenly distributed in genes except for the beginning and end, which were somewhat overrepresented. The flanking regions in eukaryotes were clearly underrepresented among suitable oligonucleotides. In addition to distributions within genes, the effects on codon and amino acid usage were also studied.

Recombination and base composition: the case of the highly self-fertilizing plant Arabidopsis thaliana

The effects of recombination and self-fertilization on base composition were investigated both theoretically and experimentally in the Arabidopsis genome. Levels of inbreeding modulate the effect of recombination on base composition.

Scaling features of noncoding DNA

We review evidence supporting the idea that the DNA sequence in genes containing noncoding regions is correlated, and that the correlation is remarkably long range — indeed, base pairs thousands of base pairs distant are correlated. We do not find such a long-range correlation in the coding regions of the gene, and utilize this fact to build a Coding Sequence Finder Algorithm, which uses statistical ideas to locate the coding regions of an unknown DNA sequence. Finally, we describe briefly some recent work adapting to DNA the Zipf approach to analyzing linguistic texts, and the Shannon approach to quantifying the “redundancy” of a linguistic text in terms of a measurable entropy function, and reporting that noncoding regions in eukaryotes display a larger redundancy than coding regions. Specifically, we consider the possibility that this result is solely a consequence of nucleotide concentration differences as first noted by Bonhoeffer and his collaborators. We find that cytosine–guanine (CG) concentration does have a strong “background” effect on redundancy. However, we find that for the purine–pyrimidine binary mapping rule, which is not affected by the difference in CG concentration, the Shannon redundancy for the set of analyzed sequences is larger for noncoding regions compared to coding regions.

An evolutionary analytical model of a complementary circular code

The subset X 0={AAC,AAT,ACC,ATC,ATT,CAG,CTC,CTG,GAA,GAC,GAG,GAT,GCC,GGC,GGT,GTA,GTC,GTT,TAC,TTC} of 20 trinucleotides has a preferential occurrence in the frame 0 (reading frame established by the ATG start trinucleotide) of protein (coding) genes of both prokaryotes and eukaryotes. This subset X 0 is a complementary maximal circular code with two permutated maximal circular codes X 1 and X 2 in the frames 1 and 2 respectively (frame 0 shifted by one and two nucleotides respectively in the 5′–3′ direction). X 0 is called a C 3 code (Arquès and Michel, 1997, J. Biosyst 44, 107–134). A quantitative study of these three subsets X 0, X 1 and X 2 in the three frames 0, 1 and 2 of eukaryotic protein genes shows that their occurrence frequencies are constant functions of the trinucleotide positions in the sequences. The frequencies of X 0, X 1 and X 2 in the frame 0 of eukaryotic protein genes are 48.5%, 29% and 22.5% respectively. These properties are not observed in the 5′ and 3′ regions of eukaryotes where X 0, X 1 and X 2 occur with variable frequencies around the random value (1/3). Several frequency asymmetries unexpectedly observed, e.g. the frequency difference between X 1 and X 2 in the frame 0, are related to a new property of the C 3 code X 0 involving substitutions. An evolutionary analytical model at three parameters ( p, q, t) based on an independent mixing of the 20 codons (trinucleotides in the frame 0) of X 0 with equiprobability (1/20) followed by t≈4 substitutions per codon according to the proportions p≈0.1, q≈0.1 and r=1− p− q≈0.8 in the three codon sites respectively, retrieves the frequencies of X 0, X 1 and X 2 observed in the three frames of protein genes and explains these asymmetries. The complex behaviour of these analytical curves is totally unexpected and a priori difficult to imagine. Finally, the evolutionary analytical method developed could be applied to the phylogenetic tree reconstruction and the DNA sequence alignment.