Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released. This sigma factor is involved in regulation of expression of heat shock genes. Intracellular concentration of free RpoH protein increases in response to heat shock, which causes association with RNA polymerase (RNAP) and initiation of transcription of heat shock genes, including numerous global transcriptional regulators and genes involved in maintaining membrane functionality and homeostasis. RpoH is then quickly degraded, leading to a decrease in the rate of synthesis of heat shock proteins and shut-off of the heat shock response. Interacts with the RNA polymerase core enzyme. Interacts with DnaK and DnaJ. Subject to complex regulation at multiple levels (transcription, translation, regulation of activity and degradation). In the absence of heat shock, or after heat shock, activity is inhibited by transient association with DnaK and DnaJ, which reduces the amounts of free active RpoH, makes it unstable and mediates its degradation by the FtsH protease. During heat shock, the intracellular concentration of RpoH increases, due to slightly increased transcription, increased synthesis and stabilization of the protein. Induction occurs mainly at the post-transcriptional level, via translational thermoregulation: at low temperature, the structure of the rpoH mRNA blocks its translation, while at high temperature, melting of the mRNA secondary structure facilitates ribosome binding and synthesis of the RpoH protein. In addition, during heat shock, stabilization of RpoH is triggered by the titration of free DnaK/DnaJ by stress-induced misfolded proteins. Can also be induced by other stress conditions, including during the first round of cell division. The sigma-70 factor domain-2 mediates sequence-specific interaction with the -10 element in promoter DNA, and plays an important role in melting the double-stranded DNA and the formation of the transcription bubble. The sigma-70 factor domain-2 mediates interaction with the RNA polymerase subunits RpoB and RpoC (By similarity). The sigma-70 factor domain-4 contains a helix-turn-helix (H-T-H) motif that mediates interaction with the -35 element in promoter DNA. The domain also mediates interaction with the RNA polymerase subunit RpoA (By similarity). Mutants exhibit an increased sensitivity to heat shock but only in the exponential phase of aerobic growth. May only be involved in heat shocks that occur during exponential phase of growth under aerobic conditions. Different mechanisms may play a prime role during stationary phase and anaerobic growth (PubMed:16775749). Belongs to the sigma-70 factor family. RpoH subfamily.