Organization and codon usage of the streptomycin operon in Micrococcus luteus, a bacterium with a high genomic G + C...

The DNA sequence of the Micrococcus luteus str operon, which includes genes for ribosomal proteins S12 (str or rpsL) and S7 (rpsG) and elongation factors (EF) G (fus) and Tu (tuf), has been determined and compared with the corresponding sequence of Escherichia coli to estimate the effect of high genomic G + C content (74%) of M. luteus on the codon usage pattern. The gene organization in this operon and the deduced amino acid sequence of each corresponding protein are well conserved between the two species. The mean G + C content of the M. luteus str operon is 67%, which is much higher than that of E. coli (51%). The codon usage pattern of M. luteus is very different from that of E. coli and extremely biased to the use of G and C in silent positions. About 95% (1,309 of 1,382) of codons have G or C at the third position. Codon GUG is used for initiation of S12, EF-G, and EF-Tu, and AUG is used only in S7, whereas GUG initiates only one of the EF-Tu's in E. coli. UGA is the predominant termination codon in M. luteus, in contrast to UAA in E. coli.