Overexpression of sgm 5’ UTR mRNA reduces gentamicin resistance in both Escherichia coli and Micromonospora melanosporea cells

The 16S rRNA methylases are expressed by most of the antibiotic producing bacteria in order to protect themselves against antibiotics by methylation of 16S rRNA at positions which are crucial for their action. The sgm sisomicin-gentamicin resistance gene from Micromonospora zionensis methylates G1405 positioned in the A site of 16S rRNA, which includes a CCGCCC hexanucleotide. The same hexanucleotide is also present 14 nucleotides in front of the ribosome binding site of sgm mRNA. The model proposed for translational regulation of sgm assumes that Sgm binds to this motif, both on 16S rRNA and on the 5’ untranslated region (UTR) of its own mRNA. The 5’ UTR mRNA sequence was overexpressed on 3’-truncated sgm mRNA, and the effect on gentamicin resistance conferred by Sgm was tested in Escherichia coli and in Micromonospora melanosporea. Overexpression of the sgm mRNA regulatory region decreases the resistance to gentamicin in both E. coli and M. melanosporea. This effect is likely to be due to titration of Sgm molecules by the overexpressed 5’ UTR