Abstact

In Gram-positive Streptomyces coelicolor A3(2), SigR (Sc σ(R)) of the group IV ECF sigma factor singly activates expression of more than 30 oxidation responsive genes. Of the two promoter-binding domains--individually called region 2 and region 4 - within Sc σ(R), we hereby report a 2.6 Å resolution structure of the -35 element interacting carboxyl-terminal region 4 (Sc σ(R)4). Structural comparison of Sc σ(R)4 with the Escherichia coli SigE (Ec σ(E)) in complex with Ec σ(E) -35 element suggested that a single residue (Sc σ(R) Met188 and Ec σ(E) Arg171) may be responsible for distinguishing the one-base pair difference of the -35 elements--Sc σ(R)(-31')ATTCC(-35') ((-31')A) vs. Ec σ(E)(-31')GTTCC(-35') ((-31')G)--by interacting with the -31'-base. Further studies using expressed Sc σ(R) indicate that the wild-type Sc σ(R) with Met188 selectively interacted with the (-31')A sequence over the (-31')G sequence, whereas a mutation of Met188 to arginine resulted in interaction with both (-31')A and (-31')G sequences. Hence, we conclude that Met188 of Sc σ(R) confers the (-31')A-selectivity in -35 element interaction by disfavoured interaction with the (-31')G base.