Predicted Highly Expressed Research Articles

Analysis of Codon Usage Pattern and Predicted Gene Expression in Neurospora Crassa: A Novel in Silico Approach

The codon usage pattern of genes has a key role in the gene expression and adaptive evolution of an organism. It is very significant in understanding the role of complex genomic structure in defining cell fates and regulating diverse biological functions. In this paper, we discussed that the codon usage index (CAIg) based on all protein-coding genes is a promising alternative to the Codon Adaptation Index (CAI). CAIg which measures the extent that a gene uses a subset of preferred codons relies exclusively on sequence features and is used as a good indicator of the strength of codon bias. A critical analysis of predicted highly expressed (PHE) genes in Neurospora crassa has been performed using codon usage index (CAIg) as a numerical estimator of gene expression level. Analyzing compositional properties and codon usage pattern of genes in Neurospora crassa, our study indicates that codon composition plays an important role in the regulation of gene expression. We found a systematic strong correlation between CAIg and CBI (codon bias index) or other expression-measures. Here, we show that codon usage index CAIg correlates well with both protein and mRNA levels; suggesting that codon usage is an important determinant of gene expression. Our study highlights the relationship between gene expression and compositional signature in relation to codon usage bias in Neurospora crassa and sets the ground for future investigation in eukaryotic biology.

Codon usage pattern and predicted gene expression in Arabidopsis thaliana.

The extensive research for predicting highly expressed genes in plant genome sequences has been going on for decades. The codon usage pattern of genes in Arabidopsis thaliana genome is a classical topic for plant biologists for its significance in the understanding of molecular plant biology. Here we have used a gene expression profiling methodology based on the score of modified relative codon bias (MRCBS) to elucidate expression pattern of genes in Arabidopsis thaliana. MRCBS relies exclusively on sequence features for identifying the highly expressed genes. In this study, a critical analysis of predicted highly expressed (PHE) genes in Arabidopsis thaliana has been performed using MRCBS as a numerical estimator of gene expression level. Consistent with previous other results, our study indicates that codon composition plays an important role in the regulation of gene expression. We found a systematic strong correlation between MRCBS and CAI (codon adaptation index) or other expression-measures. Additionally, MRCBS correlates well with experimental gene expression data. Our study highlights the relationship between gene expression and compositional signature in relation to codon usage bias and sets the ground for the further investigation of the evolution of the protein-coding genes in the plant genome.

Analyzing Gene Expression and Codon Usage Bias in Diverse Genomes Using a Variety of Models

Synonymous codon usage has long been known as a factor that affects the average expression level of proteins in microorganisms. A systematic approach to study the role of codon usage bias underlying gene expression has been described. Facts and ideas presented in this short review are to derive biological information from genome sequences by means of various statistical analyses and appropriate design of algorithms. Using codon usage bias as a numerical estimator of gene expression, a comparative analysis of predicted highly expressed (PHE) genes was performed in bacteria, cyanobacteria, archaea, lower eukaryotes and higher eukaryotes. Here, it is suggested that both codon usage and as well as base compositions at three codon sites regulate the individual gene expression. Any correlation between gene length and expression level, however, remains unexplained. Relationship between gene expression levels and synonymous codon usage provides an important line of evidence for translational selection and suggests some general mechanism underlying protein evolution. Keywords: Archaea, bacteria, codon usage, eukaryotes, GC content, gene expression, highly expressed genes predicted.

Theoretical analyses of gene expression for five human pathogens

Predicted highly expressed (PHX) genes were analyzed in five human pathogens with significant translation selection measured by within-group correspondence analysis (WCA). Functional analysis showed that in the five genomes PHX genes involved in protein synthesis, constitute the largest functional category, followed by categories of energy metabolism and protein fate. The gene encoding pyruvate kinase involved in glycolysis was PHX gene in most genomes except Bacillus anthracis Ames, which preferred strictly aerobic environment. Special PHX genes were also found, such as genes encoding phosphotransferase (PTS) system mainly appeared in Streptococcus pneumoniae genome. The analysis of virulence factors indicates that only a few pathogenicity-related genes were predicted as PHX. This is contrary to previous observations of phytopathogens, where most virulence related genes were PHX. The PHX genes may provide potential drug targets for the design of new bactericide. Specially, PHX virulence factors may help for the understanding of the crucial mechanism of virulence of the bacterial pathogens when invading human body. Key words: Highly expressed genes, human pathogen, E(g) measure, CAI; virulence related genes, inorganic pyrophosphatase.

Gene Expression Analysis of Four Radiation-resistant Bacteria.

To investigate the general radiation-resistant mechanisms of bacteria, bioinformatic method was employed to predict highly expressed genes for four radiation-resistant bacteria, i.e. Deinococcus geothermalis (D. geo), Deinococcus radiodurans (D. rad), Kineococcus radiotolerans (K. rad) and Rubrobacter xylanophilus (R. xyl). It is revealed that most of the three reference gene sets, i.e. ribosomal proteins, transcription factors and major chaperones, are generally highly expressed in the four bacteria. Recombinase A (recA), a key enzyme in recombinational repair, is predicted to be highly or marginally highly expressed in the four bacteria. However, most proteins associated with other repair systems show low expression levels. Some genes participating in 'information storage and processing,' 'cellular processes and signaling' and 'metabolism' are among the top twenty predicted highly expressed (PHX) genes in the four genomes. Many antioxidant enzymes and proteases are commonly highly expressed in the four bacteria, indicating that these enzymes play important roles in resisting irradiation. Finally, a number of 'hypothetical genes' are among the top twenty PHX genes in each genome, some of them might contribute vitally to resist irradiation. Some of the prediction results are supported by experimental evidence. All the above information not only helps to understand the radiation-resistant mechanisms but also provides clues for identifying new radiation-resistant genes from these bacteria.

Comparative analysis of predicted gene expression among deep-sea genomes

Deep-sea species live in an environment that is specifically characterized by extreme temperature and hydrostatic pressure. In this work, predicted highly expressed (PHX) genes are comparatively analyzed for six deep-sea microbes, which allows us to pinpoint the common highly expressed genes shared by them. The relationships between gene expression level and some basic properties such as genomic G + C content, optimal growth temperature (OGT), and environmental hydrostatic pressure of the six deep-sea species are also investigated. We find that the percentage of PHX genes out of a whole genome positively correlates to OGT for the deep-sea genomes, whereas such positive correlation seems not to exist between environmental hydrostatic pressure and percentage of PHX genes. Moreover, there exists a negative correlation between genomic G + C content and diversity of gene expression level for the deep-sea genomes, which is in sharp contrast to land-living microbes. We report the top 20 PHX genes for the six deep-sea genomes and find no common highly expressed genes shared by them except for ribosomal proteins, transcription factors, and translation factors. Our present work proffers a paradigm for studying the relationship between environmental factors and microbes' predicted gene expression level.

Predicted highly expressed genes in Nocardia farcinica and the implication for its primary metabolism and nocardial virulence

Nocardia farcinica is a Gram positive, filamentous bacterium, and is considered an opportunistic pathogen. In this study, the highly expressed genes in N. farcinica were predicted using the codon adaptation index (CAI) as a numerical estimator of gene expressivity. Using ribosomal protein (RP) genes as references, the top approximately approximately 10% of the genes were predicted to be the predicted highly expressed (PHX) genes in N. farcinica using a CAI cutoff of greater than 0.73. Consistent with earlier analysis of Streptomyces genomes, most of the PHX genes in N. farcinica were involved in various 'house-keeping' functions important for cell growth. However, 15 genes putatively involved in nocardial virulence were predicted as PHX genes in N. farcinica, which included genes encoding four Mce proteins, cyclopropane fatty acid synthase which is involved in the modification of cell wall which may be important for nocardia virulence, polyketide synthase PKS13 for mycolic acid synthesis and a non-ribosomal peptide synthetase involved in biosynthesis of a mycobactin-related siderophore. In addition, multiple genes involved in defense against reactive oxygen species (ROS) produced by the phagocyte were predicted with high expressivity, which included alkylhydroperoxide reductase (ahpC), catalase (katG), superoxide dismutase (sodF), thioredoxin, thioredoxin reductase, glutathione peroxidase, and peptide methionine sulfoxide reductase, suggesting that combating against ROS is essential for survival of N. farcinica in host cells. The study also showed that the distribution of PHX genes in the N. farcinica circular chromosome was uneven, with more PHX genes located in the regions close to replication initiation site. The results provided the first estimates of global gene expression patterns in N. farcinica, which will be useful in guiding experimental design for further investigations.

Genomic comparisons among γ‐proteobacteria

Predicted highly expressed (PHX) genes are compared for 16 gamma-proteobacteria and their similarities and differences are interpreted with respect to known or predicted physiological characteristics of the organisms. Predicted highly expressed genes often reflect the organism's predominant lifestyle, habitat, nutrition sources and metabolic propensities. This technique allows to predict principal metabolic activities of the microorganisms operating in their natural habitats. Among our findings is an unusually high number of PHX enzymes acting in cell wall biosynthesis, amino acid biosynthesis and replication in the ant endosymbiont Blochmannia floridanus. We ascribe the abundance of these PHX genes to specific aspects of the relationship between the bacterium and its host. Xanthomonas campestris is unique with a very high number of PHX genes acting in flagellum biosynthesis, which may play a special role during its pathogenicity. Shewanella oneidensis possesses three protein complexes which all can function as complex I in the respiratory chain but only the Na(+)-transporting NADH:ubiquinone oxidoreductase nqr-2 operon is PHX. The PHX genes of Vibrio parahaemolyticus are consistent with the microorganism's adaptation to extremely fast growth rates. Comparative analysis of PHX genes from complex environmental genomic sequences as well as from uncultured pathogenic microbes can provide a novel, useful tool to predict global flux of matter and key intermediates.

Predicted highly expressed genes in the genomes of Streptomyces coelicolor and Streptomyces avermitilis and the implications for their metabolism

Highly expressed genes in bacteria often have a stronger codon bias than genes expressed at lower levels, due to translational selection. In this study, a comparative analysis of predicted highly expressed (PHX) genes in the Streptomyces coelicolor and Streptomyces avermitilis genomes was performed using the codon adaptation index (CAI) as a numerical estimator of gene expression level. Although it has been suggested that there is little heterogeneity in codon usage in G+C-rich bacteria, considerable heterogeneity was found among genes in these two G+C-rich Streptomyces genomes. Using ribosomal protein genes as references, approximately 10% of the genes were predicted to be PHX genes using a CAI cutoff value of greater than 0.78 and 0.75 in S. coelicolor and S. avermitilis, respectively. The PHX genes showed good agreement with the experimental data on expression levels obtained from proteomic analysis by previous workers. Among 724 and 730 PHX genes identified from S. coelicolor and S. avermitilis, 368 are orthologue genes present in both genomes, which were mostly 'housekeeping' genes involved in cell growth. In addition, 61 orthologous gene pairs with unknown functions were identified as PHX. Only one polyketide synthase gene from each Streptomyces genome was predicted as PHX. Nevertheless, several key genes responsible for producing precursors for secondary metabolites, such as crotonyl-CoA reductase and propionyl-CoA carboxylase, and genes necessary for initiation of secondary metabolism, such as adenosylmethionine synthetase, were among the PHX genes in the two Streptomyces species. The PHX genes exclusive to each genome, and what they imply regarding cellular metabolism, are also discussed.

Gene expression analysis of six GC-rich Gram-negative phytopathogens

Predicted highly expressed (PHX) genes are comparatively analyzed for six GC-rich Gram-negative phytopathogens, i.e., Ralstonia solanacearum, Agrobacterium tumefaciens, Xanthomonas campestris pv. campestris ( Xcc), Xanthomonas axonopodis pv. citri ( Xac), Pseudomonas syringae pv. tomato, and Xylella fastidiosa. Enzymes involved in energy metabolism, such as ATP synthase, and genes involved in TCA cycle, are PHX in most bacteria except X. fastidiosa, which prefers an anaerobic environment. Most pathogenicity-related factors, including flagellar proteins and some outer membrane proteins, are PHX, except that flagellar proteins are missing in X. fastidiosa which is spread by insects and does not need to move during invasion. Although type III secretion system apparatus are homologous to flagellar proteins, none of them is PHX, which support the viewpoint that the two types of genes have evolved independently. Furthermore, it is revealed that some biosynthesis-related enzymes are highly expressed in certain bacteria. The PHX genes may provide potential drug targets for the design of new bactericide.

Relationship between codon biased genes, microarray expression values and physiological characteristics of Streptococcus pneumoniae.

A codon-profile strategy was used to predict gene expression levels in Streptococcus pneumoniae. Predicted highly expressed (PHE) genes included those encoding glycolytic and fermentative enzymes, sugar-conversion systems and carbohydrate-transporters. Additionally, some genes required for infection that are involved in oxidative metabolism and hydrogen peroxide production were PHE. Low expression values were predicted for genes encoding specific regulatory proteins like two-component systems and competence genes. Correspondence analysis localized 484 ORFs which shared a distinctive codon profile in the right horn. These genes had a mean G+C content (33.4 %) that was lower than the bulk of the genome coding sequences (39.7 %), suggesting that many of them were acquired by horizontal transfer. Half of these genes (242) were pseudogenes, ORFs shorter than 80 codons or without assigned function. The remaining genes included several virulence factors, such as capsular genes, iga, lytB, nanB, pspA, choline-binding proteins, and functions related to DNA acquisition, such as restriction-modification systems and comDE. In order to compare predicted translation rate with the relative amounts of mRNA for each gene, the codon adaptation index (CAI) values were compared with microarray fluorescence intensity values following hybridization of labelled RNA from laboratory-grown cultures. High mRNA amounts were observed in 32.5 % of PHE genes and in 64 % of the 25 genes with the highest CAI values. However, high relative amounts of RNA were also detected in 10.4 % of non-PHE genes, such as those encoding fatty acid metabolism enzymes and proteases, suggesting that their expression might also be regulated at the level of transcription or mRNA stability under the conditions tested. The effects of codon bias and mRNA amount on different gene groups in S. pneumoniae are discussed.

Characterizations of Highly Expressed Genes of Four Fast-Growing Bacteria

Predicted highly expressed (PHX) genes are characterized for the completely sequenced genomes of the four fast-growing bacteria Escherichia coli, Haemophilus influenzae, Vibrio cholerae, and Bacillus subtilis. Our approach to ascertaining gene expression levels relates to codon usage differences among certain gene classes: the collection of all genes (average gene), the ensemble of ribosomal protein genes, major translation/transcription processing factors, and genes for polypeptides of chaperone/degradation complexes. A gene is predicted highly expressed (PHX) if its codon frequencies are close to those of the ribosomal proteins, major translation/transcription processing factor, and chaperone/degradation standards but strongly deviant from the average gene codon frequencies. PHX genes identified by their codon usage frequencies among prokaryotic genomes commonly include those for ribosomal proteins, major transcription/translation processing factors (several occurring in multiple copies), and major chaperone/degradation proteins. Also PHX genes generally include those encoding enzymes of essential energy metabolism pathways of glycolysis, pyruvate oxidation, and respiration (aerobic and anaerobic), genes of fatty acid biosynthesis, and the principal genes of amino acid and nucleotide biosyntheses. Gene classes generally not PHX include most repair protein genes, virtually all vitamin biosynthesis genes, genes of two-component sensor systems, most regulatory genes, and most genes expressed in stationary phase or during starvation. Members of the set of PHX aminoacyl-tRNA synthetase genes contrast sharply between genomes. There are also subtle differences among the PHX energy metabolism genes between E. coli and B. subtilis, particularly with respect to genes of the tricarboxylic acid cycle. The good agreement of PHX genes of E. coli and B. subtilis with high protein abundances, as assessed by two-dimensional gel determination, is verified. Relationships of PHX genes with stoichiometry, multifunctionality, and operon structures are also examined. The spatial distribution of PHX genes within each genome reveals clusters and significantly long regions without PHX genes.

Predicted highly expressed and putative alien genes of Deinococcus radiodurans and implications for resistance to ionizing radiation damage.

Predicted highly expressed (PHX) and putative alien genes determined by codon usages are characterized in the genome of Deinococcus radiodurans (strain R1). Deinococcus radiodurans (DEIRA) can survive very high doses of ionizing radiation that are lethal to virtually all other organisms. It has been argued that DEIRA is endowed with enhanced repair systems that provide protection and stability. However, predicted expression levels of DNA repair proteins with the exception of RecA tend to be low and do not distinguish DEIRA from other prokaryotes. In this paper, the capability of DEIRA to resist extreme doses of ionizing and UV radiation is attributed to an unusually high number of PHX chaperone/degradation, protease, and detoxification genes. Explicitly, compared with all current complete prokaryotic genomes, DEIRA contains the greatest number of PHX detoxification and protease proteins. Other sources of environmental protection against severe conditions of UV radiation, desiccation, and thermal effects for DEIRA are the several S-layer (surface structure) PHX proteins. The top PHX gene of DEIRA is the multifunctional tricarboxylic acid (TCA) gene aconitase, which, apart from its role in respiration, also alerts the cell to oxidative damage.

Highly expressed and alien genes of the Synechocystis genome.

Comparisons of codon frequencies of genes to several gene classes are used to characterize highly expressed and alien genes on the SYNECHOCYSTIS: PCC6803 genome. The primary gene classes include the ensemble of all genes (average gene), ribosomal protein (RP) genes, translation processing factors (TF) and genes encoding chaperone/degradation proteins (CH). A gene is predicted highly expressed (PHX) if its codon usage is close to that of the RP/TF/CH standards but strongly deviant from the average gene. Putative alien (PA) genes are those for which codon usage is significantly different from all four classes of gene standards. In SYNECHOCYSTIS:, 380 genes were identified as PHX. The genes with the highest predicted expression levels include many that encode proteins vital for photosynthesis. Nearly all of the genes of the RP/TF/CH gene classes are PHX. The principal glycolysis enzymes, which may also function in CO(2) fixation, are PHX, while none of the genes encoding TCA cycle enzymes are PHX. The PA genes are mostly of unknown function or encode transposases. Several PA genes encode polypeptides that function in lipopolysaccharide biosynthesis. Both PHX and PA genes often form significant clusters (operons). The proteins encoded by PHX and PA genes are described with respect to functional classifications, their organization in the genome and their stoichiometry in multi-subunit complexes.

Predicted highly expressed genes of diverse prokaryotic genomes.

Our approach in predicting gene expression levels relates to codon usage differences among gene classes. In prokaryotic genomes, genes that deviate strongly in codon usage from the average gene but are sufficiently similar in codon usage to ribosomal protein genes, to translation and transcription processing factors, and to chaperone-degradation proteins are predicted highly expressed (PHX). By these criteria, PHX genes in most prokaryotic genomes include those encoding ribosomal proteins, translation and transcription processing factors, and chaperone proteins and genes of principal energy metabolism. In particular, for the fast-growing species Escherichia coli, Vibrio cholerae, Bacillus subtilis, and Haemophilus influenzae, major glycolysis and tricarboxylic acid cycle genes are PHX. In Synechocystis, prime genes of photosynthesis are PHX, and in methanogens, PHX genes include those essential for methanogenesis. Overall, the three protein families-ribosomal proteins, protein synthesis factors, and chaperone complexes-are needed at many stages of the life cycle, and apparently bacteria have evolved codon usage to maintain appropriate growth, stability, and plasticity. New interpretations of the capacity of Deinococcus radiodurans for resistance to high doses of ionizing radiation is based on an excess of PHX chaperone-degradation genes and detoxification genes. Expression levels of selected classes of genes, including those for flagella, electron transport, detoxification, histidine kinases, and others, are analyzed. Flagellar PHX genes are conspicuous among spirochete genomes. PHX genes are positively correlated with strong Shine-Dalgarno signal sequences. Specific regulatory proteins, e.g., two-component sensor proteins, are rarely PHX. Genes involved in pathways for the synthesis of vitamins record low predicted expression levels. Several distinctive PHX genes of the available complete prokaryotic genomes are highlighted. Relationships of PHX genes with stoichiometry, multifunctionality, and operon structures are discussed. Our methodology may be used complementary to experimental expression analysis.