Correlation between the 32-kDa sigma factor levels and in vitro expression of Escherichia coli heat shock genes.

Abstract
S-30 extracts from Escherichia coli cells were used to express heat shock (HS) and non-HS genes in vitro in a DNA-directed protein synthesis system. The S-30 extracts prepared from cells that have been shifted to 45.degree.C express HS genes in vitro .apprxeq. 8 times better than extracts from cells at 33.degree.C. In contrast, the expression of non-HS genes in extracts from heat-induced cells is only 40% of that seen in extracts from cells at 33.degree.C. These results correlate well with the levels of HS .sigma. factor and normal .sigma. factor bound to RNA polymerase. Thus, there was an 8-fold increase in the HS .sigma. factor and a 60% decrease in the normal .sigma. factor associated with RNA polymerase at the higher temperature. Part of the increase in the level of the HS .sigma. factor could be accounted for by a 3-fold increase in the level of HS .sigma. factor mRNA during heat induction.