Protein kinase I of Mycobacterium tuberculosis: cellular localization and expression during infection of macrophage-like cells.

Protein kinase I of Mycobacterium tuberculosis, which has an unusual amino acid composition in its catalytic loop, displayed autophosphorylation and transphosphorylation activity. Immunoblot analysis of sub-cellular fractions of M. tuberculosis, using anti-PknI antibodies raised in rabbits, showed that PknI localizes to the bacterial cytosol. In contrast, PknA was membrane-bound. Relative expression of pknI, when measured by combining molecular beacons and RT-PCR, decreased during infection of THP-1 human macrophages. Expression of pknA and pknB was upregulated during infection. Thus PknI represents a group of protein kinases that is distinct from the more extensively studied enzymes PknA and PknB.