Al. Decatur et R. Losick, 3 SITES OF CONTACT BETWEEN THE BACILLUS-SUBTILIS TRANSCRIPTION FACTORSIGMA(F) AND ITS ANTISIGMA FACTOR SPOIIAB, Genes & development, 10(18), 1996, pp. 2348-2358
The developmental regulatory protein sigma(F) of Bacillus subtilis, a
member of the sigma(70)-family of RNA polymerase sigma factors, is reg
ulated negatively by the antisigma factor SpoIIAB, which binds to sigm
a(F) to form an inactive complex. Complex formation between SpoIIAB, w
hich contains an inferred adenosine nucleotide binding pocket, and sig
ma(F) is stimulated strongly by the presence of ATP. Here we report th
at SpoIIAB contacts sigma(F) at three widely spaced binding surfaces c
orresponding to conserved regions 2.1, 3.1, and 4.1 of sigma(70)-like
sigma factors. This conclusion is based on binding studies between Spo
IIAB and truncated portions of sigma(F), the isolation of mutants of s
igma(F) that were partially resistant to inhibition by SpoIIAB in vivo
and were defective in binding to the antisigma factor in vitro, and t
he creation of alanine substitution mutants of regions 2.1, 3.1, or 4.
1 of sigma(F) that were impaired in complex formation. Because the int
eraction of SpoIIAB with all three binding surfaces was stimulated by
ATP, we infer that ATP induces a conformational change in SpoIIAB that
is needed for tight binding to sigma(F). Finally, we discuss the poss
ibility that another antisigma factor, unrelated to SpoIIAB, may inter
act with its respective sigma factor in a similar topological pattern
of widely spaced binding surfaces located in or near conserved regions
2.1, 3.1, and 4.1.