Analysis of Codon Usage Patterns in the Human Papillomavirus Oncogenes

Abstract

Background: Persistent high-risk genital human papillomavirus (HPV) infection is a major cause of cervical cancer in women. The products of the viral transforming genes E6 and E7 in the high-risk HPVs are known to be similar in their amino acid composition and structure. We performed a comparative analysis of codon usage patterns in the E6 and E7 genes of HPVs. Methods: The E6 and E7 gene sequences of eight HPV subtypes were analyzed to determine their nucleotide composition, relative synonymous codon usage (RSCU), effective number of codons (ENC), neutrality, genetic variability, selection pressure, and codon adaptation index (CAI). Additionally, a correspondence analysis (CoA) was performed. Results: The analysis to determine the effects of differences in composition on the codon usage patterns revealed that there may be usage bias for ‘A’ nucleotides. This was consistent with the results of the RSCU analysis, which demonstrated that the selection of A/T-rich patterns and the preference for A/T-ended codons in HPVs are influenced by compositional constraints. Moreover, the results reveal that selection pressure plays an important role in the CoA results for the RSCU values, Tajima’s D tests, and neutrality tests. Conclusion: The results of this study are consistent with previous findings that most papillomavirus genes are under purifying selection pressure, which limits changes to the encoded proteins. Natural selection and mutation pressures resulting in changes in the nucleotide composition and codon usage bias in the two tumor genes of HPV act differently during the evolution of the HPV subtype; thus, throughout the viral life cycle, HPV can constantly evolve to adapt to a new environment.

The evolutionary and genetic patterns of African swine fever virus

“…Thus, for ASFV, synonymous codon usage for speci c amino acids varies signi cantly between genes or genotypes, suggesting nucleotide composition and codon usage bias to be the main drivers of ASFV evolution. Furthermore, A224L and EP153R were under little selection pressure, suggesting that the strong selection of preferred codons in EP153R, which had the highest synonymous codon usage bias, may be due to nucleotide compositional constraints caused by mutation pressure on ASFV genes or genotypes [42][43][44]. Regarding overall codon usage pattern, EP153R had the lowest average ENC value (34.58), which was different from that of B646L (54.06).…”