A STATIONARY-PHASE STRESS-RESPONSE SIGMA-FACTOR FROM MYCOBACTERIUM-TUBERCULOSIS

Alternative RNA polymerase sigma factors are a common means of coordin ating gene regulation in bacteria, Using PCR amplification with degene rate primers, we identified and cloned a sigma factor gene, sigF, from Mycobacterium tuberculosis, The deduced protein encoded by sigF shows significant similarity to SigF sporulation sigma factors from Strepto myces coelicolor and Bacillus subtilis and to SigB, a stress-response sigma factor, from B. subtilis. Southern blot surveys with a sigF-spec ific probe identified cross-hybridizing bands in other slow-growing my cobacteria, Mycobacterium bovis bacille Calmette-Guerin (ECG) and Myco bacterium avium, but not in the rapid-growers Mycobacterium smegmatis or Mycobacterium abscessus. RNase protection assays revealed that M. t uberculosis sigF mRNA Is not present during exponential-phase growth i n M. bovis BCG cultures but is strongly induced during stationary phas e, nitrogen depletion, and cold shock, Weak expression of M. tuberculo sis sigF was also detected during late-exponential phase, oxidative st ress, anaerobiasis, and alcohol shock, The specific expression of M. t uberculosis sigF during stress or stationary phase suggests that it ma y play a role in the ability of tubercle bacilli to adapt to host defe nses and persist during human infection.