Abstract
Derivatives of the stationary-phase sigma factor σ
S
of
Escherichia coli
lacking either of two conserved domains, the postulated N-terminal subregion 1.1 or the C-terminal region 4, were shown to be competent in vitro for transcription initiation from several σ
S
-dependent promoters on supercoiled DNA templates. Unlike wild-type σ
S
, however, the deletion derivatives were inactive on relaxed templates. The anomalous slow electrophoretic mobility of σ
S
on denaturing gels was corrected by deletion of subregion 1.1, suggesting that this domain in σ
S
may be structurally and functionally analogous to subregion 1.1 of σ
70
, substitutions in which have previously been shown to rectify the anomalous electrophoretic migration of σ
70
(V. Gopal and D. Chatterji, Eur. J. Biochem. 244:614-618, 1997).
