Mycobacterium tuberculosis SigF Regulates Genes Encoding Cell Wall-Associated Proteins and Directly Regulates the Transcriptional Regulatory Gene phoY1

Mycobacterium tuberculosis SigF is homologous to stress response and sporulation sigma factors in many bacteria. Consistent with a possible role in mycobacterial survival under stress conditions,M. tuberculosis sigF is strongly induced within cultured human macrophages and upon nutrient starvation, and SigF has been implicated inM. tuberculosis entry into stationary phase. On the other hand, SigF appears to contribute to the immune pathology of tuberculosis (TB), and asigF -deficient mutant has altered cell membrane properties. Using anM. tuberculosis sigF deletion mutant, we show here thatsigF is not required for bacillary survival under nutrient starvation conditions and within activated murine macrophages or for extracellular persistence in an in vivo granuloma model of latent TB infection. Using a chemically inducible recombinant strain to conditionally overexpresssigF , we did not observe arrest or retardation of growth in exponentially growing cultures or reduced susceptibility to rifampin and isoniazid. Consistent with our hypothesis that SigF may mediate TB immunopathogenesis by altering cell membrane properties, we found that overexpression ofsigF resulted in the differential regulation of many cell wall-associated proteins, including members of the MmpL, PE, and PPE families, several of which have been shown to influence host-pathogen interactions. The most highly upregulated gene by quantitative reverse transcription-PCR at all time points followingsigF induction was Rv3301c (phoY1 ), which encodes a probable transcriptional regulatory protein homologous to PhoU proteins involved in regulation of phosphate uptake. Using in vitro transcription analysis, we show that SigF directly regulatesphoY1 , whose proposed promoter sequence is GGATTG-N16 -GGGTAT.