Codon preference in corynebacteria.

The codon usage (CU) of 34 genes from the closely related species, Brevibacterium lactofermentum and Corynebacterium glutamicum (BLCG), was analysed and compared with that of 23 genes from other Brevibacterium and Corynebacterium species. The G+C content of the BLCG genes ranged from 50 to 62%. A wider range was found in other corynebacterial genes (25-71%). The G+C contents of non-coding regions in glutamic acid bacteria are lower than those of the coding regions and both values are lower than the G+C content of ribosomal RNA (rRNA) sequences, suggesting an unusual biased mutation pressure. The CU and synonymous codon usage (SCU) analysis showed several common characteristics among the sequenced corynebacterial genes, consistent with the close relatedness of B. lactofermentum and C. glutamicum. A subset of 25 preferred codons were deduced from the presumably highly expressed genes and they encode most of the amino acid (aa) residues of the BLCG group. An analysis of the effective number of codons (Nc) was carried out in order to check the GC3s (G+C content at the silent third position of sense codons) dependence of the CU in corynebacteria. Nc values showed differences between the BLCG group and other corynebacterial sequences. A comparison of the most used codons for each aa showed a stronger similarity to Streptomyces than to Escherichia coli. The CU/SCU tables of corynebacteria are useful for identification of protein-coding regions, including start codons when they are uncertain, and for designing oligodeoxyribonucleotide probes from an aa sequence.