FIG. 4.

Decreased atl transcription and increased protease activity in the pknB mutant contribute to its autolytic phenotype. (A) Northern blot analysis of stationary-phase cells showing the transcriptions of atl and spl (carrying a serine protease operon) in the pknB mutant in comparison with the levels in the parent and the complemented strain. (B) Protease activity in the supernatants of stationary-phase cells as assessed by an Enz-Chek Bodipy fluorescence kit. AU, arbitrary units. (C) Bacteriolytic activity of supernatants taken from stationary-phase cultures of different constructs grown in the presence of 1 mM PMSF using heat-killed USA300 as the substrate.