A SERINE THREONINE PROTEIN-KINASE FROM MYCOBACTERIUM-TUBERCULOSIS/

Genomic DNA sequencing in the vicinity of the pstA-1 gene from Mycobac terium tuberculosis allowed us to clone, sequence and identify a gene encoding a 70-kDa protein. The size of the protein was confirmed by in vitro coupled transcription/translation. Its N-terminal domain shows extensive sequence similarity with the catalytic domain of eukaryotic serine/threonine protein kinases, and the protein was therefore called Mbk (mycobacterial protein kinase). The deduced amino acid sequence c ontains two transmembrane segments, which flank a highly repetitive re gion, suggesting a receptor-like anchoring. The mbk gene was overexpre ssed in Escherichia coli and the gene product (Mbk) was purified as a fusion protein with gluthatione S-transferase. Recombinant Mbk was fou nd to be autophosphorylated on threonine residues and capable of phosp horylating myelin basic proteins from bovine brain and histones from c alf thymus on serine residues, both in a manganese-dependent manner. T he phosphorylation of myelin basic proteins by Mbk was inhibited by ca lcium and by staurosporine, a widely used inhibitor of eukaryotic prot ein serine/threonine kinases. A similar gene was found in Mycobacteriu m bovis BCG DNA by Southern blot analysis. Its expression was detected in cultures of M. bovis BCG by reverse transcriptase/PCR. Although it s biological role is unknown, it is the first serine/threonine protein kinase characterized in Mycobacteria.