Practice question

Sigma70, encoded by rpoD, is the primary housekeeping sigma factor of Escherichia coli and most Gram-negative bacteria active during exponential growth. It directs RNA polymerase to the majority of promoters driving essential genes for central metabolism, ribosome synthesis, and cell envelope production, recognizing consensus -35 TTGACA and -10 TATAAT sequences. Housekeeping activity ensures continuous expression of vegetative functions. Under stress or developmental change, alternative sigma factors such as sigma32 for heat shock, sigma38 for general stress, sigma28 for flagella, and sigma54 for nitrogen assimilation displace sigma70.