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At least 19 recordsLinked to original sources

PubMed1991

Codon usage in Aspergillus nidulans.

Synonymous codon usage in genes from the ascomycete (filamentous) fungus Aspergillus nidulans has been investigated. A total of 45 gene sequences has been analysed. Multivariate statistical analysis has been used to identify a single major trend among genes. At one end of this trend are lowly expressed genes, whereas at the other extreme lie genes known or expected to be highly expressed. The major trend is from nearly random codon usage (in the lowly expressed genes) to codon usage that is highly biased towards a set of 19-20 "optimal" codons. The G + C content of the A. nidulans genome is close to 50%, indicating little overall mutational bias, and so the codon usage of lowly expressed genes is as expected in the absence of selection pressure at silent sites. Most of the optimal codons are C- or G- ending, making highly expressed genes more G + C-rich at silent sites.

Aspergillus nidulans↗

PubMed1992

Codon usage in Entamoeba histolytica.

The codon usage of 10 E. histolytica genes comprising 4455 codons was analysed. The codon usage revealed an extremely biased use of synonymous codons with a preference for NNU (44%) and NNA (41.4%) codons. Codons CGG (arg), AGG (arg) and CCG (pro) were absent in the E. histolytica genes examined. The codon usage of E. histolytica resembled that of Plasmodium falciparum.

Animals↗

PubMedDate not supplied

Codon usage in Giardia lamblia.

A codon usage table for the intestinal parasite Giardia lamblia was generated by analysis of the nucleotide sequences of eight genes comprising 3,135 codons. Codon usage revealed a biased use of synonymous codons with a preference for NNC codons (42.1%). The codon usage of G. lamblia more closely resembles that of the prokaryote Halobacterium halobium (correlation coefficient r = 0.73) rather than that of other eukaryotic protozoans, i.e. Trypanosoma brucei (r = 0.434) and Plasmodium falciparum (r = -0.31). These observations are consistent with the view that G. lamblia represents the first line of descent from the ancestral cells that first took on eukaryotic features.

Animals↗

PubMed2025

Codon usage of human DNA viruses and its similarity to certain host genes.

Codon usages of DNA viruses had previously been shown to associate with their genome size. Codon usage of various human DNA viruses was compared to those of human genes to further understand viral codon usage and its roles in viral-host interaction. Codon usage bias in both large and small genome human DNA viruses was dominantly driven by translation selection. Non-optimal codon usage in small DNA viruses showed similarity to cell cycle-related genes, whereas codon usage of large DNA viruses was more diverse, herpesviruses showed more heterogeneity than human adenoviruses, while poxviruses showed a clear bimodal pattern. Some of the large DNA viruses such as herpes simplex and molluscum contagiosum viruses showed more optimal codon usage. Enrichment analysis identified some groups of human genes with similar codon usage to each group of these viruses. These host genes with similarity in codon usages to those of viruses may be efficiently expressed in infected cells and involved in their life cycle, pathogenesis and/or immune evasion.

Humans↗

PubMed2026

Mitochondrial genomes of Dactylogyrus wunderi (Monopisthocotyla: Dactylogyridae): structural features, codon usage patterns, and phylogenetic implications.

BACKGROUND: Codon usage bias (CUB) is a common phenomenon reported among many species and genes, but its unique characteristics in the mitochondrial genome of class Monopisthocotyla remain unknown. METHODS: The complete mitochondrial genome of Dactylogyrus wunderi was sequenced and characterized, and the mitochondrial genome compositions and CUB of six Dactylogyrus species and 35 Monopisthocotyla species were analyzed using bioinformatics methods. RESULTS: The mitochondrial genome of D. wunderi is a typical circular structure in length of 14,920 bp. The A + T contents of the six Dactylogyrus species (58.4% ± 5.7%) were significantly lower than that of Monopisthocotyla species (71.0% ± 5.80%, p < 0.01). Neutrality plot analysis showed slopes of 0.3136 and 0.389 in the six Dactylogyrus and the 35 Monopisthocotyla species, respectively. Furthermore, 98.3% and 77.4% of the genes in the six Dactylogyrus and the Monopisthocotyla species, respectively, had effective number of codons (ENC) higher than 35, but 23.3% and 0.5% genes of ENC ratio ranged from - 0.05 to 0.05 in the six Dactylogyrus and Monopisthocotyla species. Phylogenetic analysis revealed that, within the context of the sampled taxa, the families of Monopisthocotyla were monophyletic groups, except for Ancyrocephalidae. CONCLUSIONS: The nucleotide composition had AT base bias in Monopisthocotyla, and natural selection was the main factor affecting CUB in the mitochondrial genomes of Monopisthocotyla species. These results provided insights into the factors affecting CUB in Monopisthocotyla species and deepened our insight of phylogeny, evolution, and codon usage of Monopisthocotyla.

Genome, Mitochondrial↗

PubMedDate not supplied

Trypanosomatidae codon usage and GC distribution.

A study of Trypanosomatidae GC distribution and codon usage is presented. The codon usage patterns in coincidence with the phylogenetical data are similar in Crithidia and Leishmania, whereas they are more divergent in Trypanosoma brucei and T. cruzi. The analysis of the GC mutational pressure in these organisms reveals that T. brucei, and to a lesser extent T. cruzi, have evolved towards a more balanced use of all bases, whereas Leishmania and Crithidia retain features of a primeval genetic apparatus. Tables with the approximated GC mutational pressure in homologous genes, and codon usage in Trypanosomatidae are presented.

Animals↗

PubMedDate not supplied

Differences in codon usage among genes encoding proteins of different function in Rhodobacter capsulatus.

Codon usage in Rhodobacter was evaluated and found to be strikingly different from that in Escherichia coli. While codon usage for genes concerned with nitrogen utilization and carotenoid biosynthesis corresponded to expectation, based on codon usage for Rhodobacter in general, that for the fructose utilization (fru) operon and for the photosynthetic genes encoding the reaction centre and light harvesting proteins exhibited significant deviation from expectation and from each other for specific amino acids. The differences in codon usage for the fru operon versus the photosynthetic genes may reflect different proportions of the various tRNA specific for certain amino acids when cells are grown under heterotrophic versus phototropic conditions. In addition, preferential use of the initiation codon, GTG, was found for the first cistrons of Rhodobacter operons.

Base Sequence↗

PubMed2026

Natural Selection Drives Codon Usage Bias in the Mitochondrial Genome of Ligula intestinalis (Linnaeus, 1758) Gmelin, 1790 (Cestoda: Diphyllobothriidea): Insights from Comparative Genomics and Optimal Codon Identification.

Codon usage bias (CUB) is a useful indicator of evolutionary forces shaping mitochondrial genomes. Codon usage bias in mitochondrial genomes of Diphyllobothriidae and especially in Ligula intestinalis was characterized. The roles of natural selection and mutation pressure in framing this bias were evaluated on the basis of 12 protein-coding genes in Diphyllobothriidae. The complete mitogenome (13,725 bp) of L. intestinalis comprises 12 protein-coding genes (PCGs), 22 tRNAs, and two rRNAs, all positioned on the heavy strand, and contains an overall AT content of 66.15%. The mean CAI (0.176), CBI (-0.105), and ENC (45.33) and an evident preference for U-ending codons observed in all examined genes indicate weak CUB. Neutrality, ENC, and PR2 plots consistently demonstrate that natural selection is the predominant force driving CUB and contributes approximately 56% in L. intestinalis and 83% in other Diphyllobothriidea species, with mutation pressure playing a secondary role. Phylogenetic reconstruction supported the monophyly of Diphyllobothriidea, confirmed the paraphyly of Diphyllobothrium as traditionally defined, and placed Ligula and Digramma as sister taxa. These findings clarify the evolutionary constraints governing codon usage in cestode mitogenomes and provide practical resources for codon optimization in heterologous gene expression and genetic studies of this economically important parasite.

Diphyllobothriidea↗

PubMed1992

Evolution of codon usage patterns: the extent and nature of divergence between Candida albicans and Saccharomyces cerevisiae.

Codon usage in a sample of 28 genes from the pathogenic yeast Candida albicans has been analysed using multivariate statistical analysis. A major trend among genes, correlated with gene expression level, was identified. We have focussed on the extent and nature of divergence between C.albicans and the closely related yeast Saccharomyces cerevisiae. It was recently suggested that significant differences exist between the subsets of preferred codons in these two species [Brown et al. (1991) Nucleic Acids Res. 19, 4293]. Overall, the genes of C.albicans are more A + T-rich, reflecting the lower genomic G + C content of that species, and presumably resulting from a different pattern of mutational bias. However, in both species highly expressed genes preferentially use the same subset of 'optimal' codons. A suggestion that the low frequency of NCG codons in both yeast species results from selection against the presence of codons that are potentially highly mutable is discounted. Codon usage in C.albicans, as in other unicellular species, can be interpreted as the result of a balance between the processes of mutational bias and translational selection. Codon usage in two related Candida species, C.maltosa and C.tropicalis, is briefly discussed.

Biological Evolution↗

PubMed2026

Comprehensive analysis of synonymous codon usage bias and evolutionary dynamics in the chloroplast genomes of eight Coptis species.

Coptis is a medically important genus renowned for producing valuable isoquinoline alkaloids. Although its chloroplast genomes encode key components for photosynthesis and plastid gene expression, the evolutionary constraints acting on their coding sequences and synonymous codon usage remain poorly resolved. Here, we combined a transparent taxon-level sampling strategy with comparative analyses of chloroplast CDSs from eight Coptis taxa. We quantified nucleotide composition, relative synonymous codon usage, effective number of codons, neutrality and PR2 patterns, and correspondence analysis, and then integrated these results with a core-CDS distance analysis and gene-wise pairwise dN/dS estimates. The chloroplast genomes showed a conserved AT-rich composition, especially at the third codon position (GC3 approximately 30.3-30.8%), with a consistent GC1 > GC2 > GC3 trend. Thirty preferred codons were detected, 28 ending in A/T, and eleven optimal codons were shared across the genus. The core-CDS distance analysis recovered a close relationship between C. chinensis and C. chinensis var. brevisepala, whereas most coding genes showed dN/dS values below one, consistent with pervasive purifying constraint. Across 48 consistently filtered CDSs, GC3s was negatively associated with mean dN (Spearman rho = -0.404, P = 0.00439) and CAI was positively associated with mean dN (rho = 0.303, P = 0.0361), whereas the remaining associations were not significant (all P > = 0.0972). These results extend codon-usage analysis by linking synonymous-site composition to coding-sequence evolution within Coptis, while providing a hypothesis-generating resource for future plastid engineering studies.

Genome, Chloroplast↗

PubMed1991

Codon usage is imposed by the gene location in the transcription unit.

A characteristic profile of the fluctuations of codon usage is observed in bacteriophages and mitochondria. By following the DNA in the direction of transcription, one moves slowly from a region where selective pressure favours codons ending with C to a region where the bias is in favour of codons ending with T; then, abruptly, one again enters a region of codons ending in C. The transcription end point takes place in the area of abrupt change in codon usage. By comparing Drosophila yakuba and mouse mitochondrial genomes, it is possible to show that the strategy of codon usage for a given gene depends on its location along the transcription unit and not on the encoded protein. The choice of codons ending in T or C allows large scale variations of DNA stability which could regulate the speed of propagation of the RNA polymerase.

Animals↗

PubMed1992

Codon usage in the G+C-rich Streptomyces genome.

The codon usage (CU) patterns of 64 genes from the Gram+ prokaryotic genus Streptomyces were analysed. Despite the extremely high overall G+C content of the Streptomyces genome (estimated at 0.74), individual genes varied in G+C content from 0.610 to 0.797, and had third codon position G+C contents (GC3s) that varied from 0.764 to 0.983. The variation in GC3s explains a significant proportion of the variation in CU patterns. This is consistent with an evolutionary model of the Streptomyces genome where biased mutation pressure has led to a high average G+C content with random variation about the mean, although the variation observed is greater than that expected from a simple binomial model. The only gene in the sample that can be confidently predicted to be highly expressed, EF-Tu of Streptomyces coelicolor A3(2) (GC3s = 0.927), shows a preference for a third position C in several of the four codon families, and for CGY and GGY for Arg and Gly codons, respectively (Y = pyrimidine); similar CU patterns are found in highly expressed genes of the G+C-rich Micrococcus luteus genome. It thus appears that codon usage in Streptomyces is determined predominantly by mutation bias, with weak translational selection operating only in highly expressed genes. We discuss the possible consequences of the extreme codon bias of Streptomyces and consider how it may have evolved. A set of CU tables is provided for use with computer programs that locate protein-coding regions.

Base Composition↗

PubMed1991

Codon usage and G + C content in Bradyrhizobium japonicum genes are not uniform.

To date, the sequences of 45 Bradyrhizobium japonicum genes are known. This provides sufficient information to determine their codon usage and G + C content. Surprisingly, B. japonicum nodulation and NifA-regulated genes were found to have a less biased codon usage and a lower G + C content than genes not belonging to these two groups. Thus, the coding regions of nodulation genes and NifA-regulated genes could hardly be identified in codon preference plots whereas this was not difficult with other genes. The codon frequency table of the highly biased genes was used in a codon preference plot to analyze the RSRj alpha 9 sequence which is an insertion sequence (IS)-like element. The plot helped identify a new open reading frame (ORF355) that escaped previous detection because of two sequencing errors. These were now corrected. The deduced gene product of ORF355 in RSRj alpha 9 showed extensive similarity to a putative protein encoded by an ORF in the T-DNA of Agrobacterium rhizogenes. The DNA sequences bordering both ORFs showed inverted repeats and potential target site duplications which supported the assumption that they were IS-like elements.

Amino Acid Sequence↗

PubMed1992

Diagrammatization of codon usage in 339 human immunodeficiency virus proteins and its biological implication.

The occurrence frequencies of bases A (adenine), C (cytosine, G (guanine), and T (thymine) occurring in the 1st, 2nd, and 3rd codon positions in the codon usage table of viral genes for the 339 human immunodeficiency virus (HIV) proteins compiled recently have been calculated and diagrammatized. For comparison, the corresponding diagrammatic representations for the 2681 human proteins from the codon usage table for primate genes are also presented. The analyzed results based on these characteristic diagrams indicate that considerably similar features have been found between HIV and human proteins for the 1st and 2nd codon positions; i.e., they are all occupied predominantly by purine, especially base A. However, a significant difference in the 3rd codon position between HIV and human proteins has been observed; i.e., human proteins are of high C + G content and low A + G content in the 3rd codon position, whereas the case is just the opposite for HIV proteins. The biological implication of such a duality on the codon bias of HIV against human proteins is discussed. It is suggested that the 1st and 2nd codon positions can be termed as the structure-determining position, and the 3rd codon position termed as the species-determining position. The diagrammatic representation and analysis method described here possess a great potential for the study of molecular evolution from the viewpoint of the genetic code for which data have been accumulated rapidly and will continue to grow at a much faster pace.

Base Composition↗

PubMed1991

The selection-mutation-drift theory of synonymous codon usage.

It is argued that the bias in synonymous codon usage observed in unicellular organisms is due to a balance between the forces of selection and mutation in a finite population, with greater bias in highly expressed genes reflecting stronger selection for efficiency of translation. A population genetic model is developed taking into account population size and selective differences between synonymous codons. A biochemical model is then developed to predict the magnitude of selective differences between synonymous codons in unicellular organisms in which growth rate (or possibly growth yield) can be equated with fitness. Selection can arise from differences in either the speed or the accuracy of translation. A model for the effect of speed of translation on fitness is considered in detail, a similar model for accuracy more briefly. The model is successful in predicting a difference in the degree of bias at the beginning than in the rest of the gene under some circumstances, as observed in Escherichia coli, but grossly overestimates the amount of bias expected. Possible reasons for this discrepancy are discussed.

Amino Acyl-tRNA Synthetases↗

PubMed1992

An analysis of the codon usage of Pasteurella haemolytica A1.

Analysis of approximately 17 kbp of nucleotide sequences from three different regions of the genome of Pasteurella haemolytica A1 showed that the mol% G+C of P. haemolytica A1 DNA is 38.5%. When only the coding sequences (approx. 10 kbp) were analysed, a similar value of 38.8% was obtained. A comparison of the relative synonymous codon usage values of the cloned genes showed that P. haemolytica A1 has a very different codon usage pattern from that of Escherichia coli.

Base Composition↗

PubMed1991

Novel anticodon composition of transfer RNAs in Micrococcus luteus, a bacterium with a high genomic G + C content. Correlation with codon usage.

The number and relative amount of isoacceptor tRNAs for each amino acid in Micrococcus luteus, a Gram-positive bacterium with high genomic G + C content, have been determined by sequencing their anticodon loop and its adjacent regions and by selective labelling of tRNAs. Thirty-one tRNA species with 29 different anticodon sequences have been detected. All the tRNAs have G or C at the anticodon first position except for tRNA(ICGArg) and tRNA(NGASer), in response to the abundant usage of NNC and NNG codons. No tRNA with the anticodon UNN capable of translating codon NNA has been detected, in accordance with a very low or zero usage of NNA codons. The relative amount of isoacceptor tRNAs for an amino acid determined by selective labelling strongly correlates with usage of the corresponding codons. On the basis of these and other observations in this and other eubacterial species, we conclude that the relative amount and anticodon composition of isoacceptor tRNA species are flexible, and their changes are mainly adaptive phenomena that have been primarily affected by codon usage, which in turn is affected by directional mutation pressure.

Anticodon↗

PubMed1990

Nucleotide sequence of the Caulobacter crescentus flaF and flbT genes and an analysis of codon usage in organisms with G + C-rich genomes.

The Caulobacter crescentus flaFG region encodes trans-acting, regulatory factors that modulate flagellin synthesis during flagellum biogenesis. In this study, sequence analysis and experiments utilizing a promoterless cat gene demonstrated that the flaF and flbT genes have overlapping transcripts with the same orientation. In addition, the 5' ends of the flgL and flbA genes were located. A sequence resembling an Rho-factor-independent terminator was found in the 3' region of the flaF gene. This region was uniquely A + T-rich and the encoded mRNA contained an inverted repeat sequence which could form a stable stem-loop structure followed by nine U-residues. The codon usage of C. crescentus genes was examined and indicated a preference for specific codons from each of the synonymous codon groups. Furthermore, comparison to the codon usage of other organisms with G + C-rich genomes indicated a strong preference for the same codons preferred by C. crescentus.

Amino Acid Sequence↗