Alternative sigma factors and two component regulatory systems

Normal sigma factor is s₇₀.

Under some conditions, this sigma can be replaced by other sigmas, so that other promoters can be recognized

Heat shock gene txn regulated by alternative sigma factors

-          if raise temp of E. coli, the cells shut off txn of many genes but induce txn of some others

-          if isolate RNAP and examine subunits on a gel, don’t see a 70kD band, but see a 32kD band

-          s₇₀ denatures and is inactive at higher temps

-          s₃₂ increases in abundance because

o       Increase in txn of its gene

o       Increase in translation of mRNA

o       Increase in stability and activity because chaperones DNAJ/K bind other denatured proteins

-          How does s₃₂ gene get transcribed?

o       Its promoter is recognized by a minor form of RNAP that has s₂₄ as its sigma factor (but only at high temp)