Pathogenic species of Mycobacterium are slowly growing intracellular bacteria. Slow growth is import-ant for the parasitism of these organisms and chronicity of the disease, but its precise mechanism has not been elucidated. Recently, we found that a novel DNA-binding protein (MDPI) was expressed (7-10% in total protein) in mycobacteria, such as Mycobacterium bovis bacillus Calmette-Guerin, Mycobacterium tuberculosis, and Mycobacterium leprae. In this study, we observed that MDPI interfered with replication, transcription, and translation in the analysis in in vitro E. coli cell-free macromolecular biosynthesizing systems. Furthermore, MDPI inhibited the rapid growth of both Escherichia coli and Mycobacterium smegmatis, and NH2-terminal second amino acid, asparagine, was observed to be important in terms of this function. These data suggest an important role of MDPI for suppression of growth rates of mycobacteria. (C) 2000 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.