The kgmB gene,encoding ribosomal RNA methylase from Streptomyces tenebrarius, is autogenously regulated

The KgmB methylase (the kanamycin–gentamicin resistance methylase from Streptomyces tenebrarius) acts at G-1405 of 16S rRNA within the sequence CGUCA that is also found 6 bp in front of ribosomal binding site of the kgmB gene. The kgmBlacZ gene and operon fusions were used in order to test for translational autoregulation of kgmB gene. Overexpression of kgmB either in cis or in trans drastically decreased the level of expression of the fusion protein. However, mutagenesis eliminated any role for the CGUCA sequence in translational autoregulation. Hence, the role of second putative regulatory sequence (CGCCC) that was shown to be involved in regulation of another methylase, Sgm (sisomicin–gentamicin methylase gene from Micromonospora zionensis) was examined. It was shown that the Sgm methylase can also decrease the level of expression of the kgmBlacZ fusion protein.