Anti-sigma factor for SigI. Negatively regulates SigI activity through direct interaction. Has no direct effect on virulence gene expression. Interacts (via RsgI N-terminal anti-sigma domain) with SigI. Part of the sigI-rsgI operon, which is induced by heat shock. Loss of rsgI results in a strong increase in sigI promoter activity in both the exponential and stationary phases.