Binding site of restriction-modification system controller protein in Mollicutes

Bacteria of the class Mollicutes underwent extreme reduction of genomes and gene expression control systems. Only a few regulators are known to date. In this work, we describe a novel group of transcriptional regulators that are distributed within different Mollicutes and control the expression of restriction-modification systems (RM-systems).

We performed cross-species search of putative regulators of RM-systems (C-proteins) and respective binding sites in Mollicutes. We identified a set of novel putative C-protein binding motifs distributed within Mollicutes. We studied the most frequent motif and respective C-protein on the model of Mycoplasma gallisepticum S6. We confirmed our prediction and identified key nucleotides important for C-protein binding. Further we identified novel target promoters of C-protein in M. gallisepticum.

We found that C-protein of M. gallisepticum binds predicted conserved direct repeats of the (GTGTTAN₅)₂ motif. Apart from its own operon promoter, HsdC can bind to the promoters of the clpB chaperone gene and a tRNA cluster.