Identification of the mycobacterial DNA-binding protein 1 region which suppresses transcription in vitro

We recently identified a novel DNA-binding protein from Mycobacterium bovis bacillus Calmette-Guérin (BCG), termed mycobacterial DNA-binding protein 1 (MDP1). MDP1 inhibited the in vitro syntheses of DNA, RNA and protein, and reduced growth rates of bacteria transformed with MDP1 genes. In this study, we examined the DNA binding regions of MDP1 by using a set of synthetic peptides. One dominant region was determined on peptide 4 composed of amino acids, at positions 31-50. The peptide 4 inhibited syntheses of both DNA and RNA in vitro. The critical amino acids residues for these functions were analysed utilizing synthetic peptides substituted with Ala. This domain was perfectly conserved in MDP1 homologues in mycobacteria, but not observed in other known DNA binding proteins. These results indicate mycobacteria possess a unique nuclear protein, which might be involved in growth regulation of these organisms.