Mapping codon usage in sequence regions flanking cleavage positions in the hepatitis A virus polyprotein.

To analyze the synonymous codon usage patterns of sequence regions flanking cleavage sites in the hepatitis A virus (HAV) polyprotein, the codon usage bias at codon positions and the synonymous codon usage in the target contexts of 30 virus strains were estimated by two simple methods that were based on the values for relative synonymous codon usage. In addition, the pattern of synonymous codon usage was compared between the genomic sequences in HAV and those of its human host. Our results indicated that HAV adopts a combination of coincidence and antagonism with the synonymous codon usage in humans. This characteristic may help HAV to efficiently use the translational machinery in its human host. We also observed that codon usage exhibited a strong bias in some specific positions in these contexts, and that the underrepresented synonymous codons, CUA for Leu, ACG for Thr, GUA for Val, and UCG for Ser, are preferentially used in these positions. These underrepresented synonymous codons likely play roles in regulating the rate of protein translation and influencing the secondary structure of the sequence regions flanking the cleavage sites.