Preferential usage of some minor codons in bacteria

In many bacterial species, such as Deinococcus radiodurans, Haemophilus influenzae, and Methanobacterium thermoautotrophicum, some minor codons are preferentially used near the initiation codon. Among these codons, there are some minor codons that have strong preference for the initiation site in the high codon adaptation index (CAI) group (comprising of highly expressed genes) rather than in the low CAI genes group (comprising of low expressing genes). In the present study, codon usage in the initiation site and in the rest of the gene was systematically compared in the 27 complete bacterial genomes and Saccharomyces cerevisiae genome. Furthermore, we classified genes into two groups according to the CAI values and conducted the same analysis for each of the two groups. Our results suggest a role for some minor codons in the initiation site of the regulating translation system in many bacteria. We have summarized codons that are preferentially used in the initiation site and probably play a role in regulating genes expression in these organisms.