Characterization of synonymous codon usage bias in the pseudorabies virus US1 gene

Codon usage and codon context bias in Xanthophyllomyces dendrorhous

Background

Synonymous codons are used differentially in organisms from the three domains of life, a phenomenon referred to as codon usage bias. In addition, codon pair bias, particularly in the 3’ codon context, has also been described in several organisms and is associated with the accuracy and rate of translation. An improved understanding of both types of bias is important for the optimization of heterologous protein expression, particularly in biotechnologically important organisms, such as the yeast Xanthophyllomyces dendrorhous, a promising bioresource for the carotenoid astaxanthin. Using genomic and transcriptomic data, the codon usage and codon context biases of X. dendrorhous open reading frames (ORFs) were analyzed to determine their expression levels, GC% and sequence lengths. X. dendrorhous totiviral ORFs were also included in these analyses.

Results

A total of 1,695 X. dendrorhous ORFs were identified through comparison with sequences in multiple databases, and the intron-exon structures of these sequences were determined. Although there were important expression variations among the ORFs under the studied conditions (different phases of growth and available carbon sources), most of these sequences were highly expressed under at least one of the analyzed conditions. Independent of the culture conditions, the highly expressed genes showed a strong bias in both codon usage and the 3’ context, with a minor association with the GC% and no relationship to the sequence length. The codon usage and codon-pair bias of the totiviral ORFs were highly variable with no similarities to the host ORFs.

Conclusions

There is a direct relation between the level of gene expression and codon usage and 3′ context bias in X. dendrorhous, which is more evident for ORFs that are expressed at the highest levels under the studied conditions. However, there is no direct relation between the totiviral ORF biases and the host ORFs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1493-5) contains supplementary material, which is available to authorized users.

Characterization of the porcine epidemic diarrhea virus codon usage bias

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Codon usage bias of porcine epidemic diarrhea virus is low.

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Mutational bias and natural selection pressure influence codon usage bias of porcine epidemic diarrhea virus.

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Natural selection plays an increasingly significant role during evolution of porcine epidemic diarrhea virus.

Porcine epidemic diarrhea virus (PEDV) has been responsible for several recent outbreaks of porcine epidemic diarrhea (PED) and has caused great economic loss in the swine-raising industry. Considering the significance of PEDV, a systemic analysis was performed to study its codon usage patterns. The relative synonymous codon usage value of each codon revealed that codon usage bias exists and that PEDV tends to use codons that end in T. The mean ENC value of 47.91 indicates that the codon usage bias is low. However, we still wanted to identify the cause of this codon usage bias. A correlation analysis between the codon compositions (A3s, T3s, G3s, C3s, and GC3s), the ENC values, and the nucleotide contents (A%, T%, G%, C%, and GC%) indicated that mutational bias plays role in shaping the PEDV codon usage bias. This was further confirmed by a principal component analysis between the codon compositions and the axis values. Using the Gravy, Aroma, and CAI values, a role of natural selection in the PEDV codon usage pattern was also identified. Neutral analysis indicated that natural selection pressure plays a more important role than mutational bias in codon usage bias. Natural selection also plays an increasingly significant role during PEDV evolution. Additionally, gene function and geographic distribution also influence the codon usage bias to a degree.