The Importance of a Proper Helical Structure in the Promoter - 10 Binding Region to Bacillus subtilis .SIGMA.A Structure and Function.

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Two Bacillus subtilis sigA mutants with amino acid substitutions tending to disrupt the structure of the promoter -10 binding helix of B. subtilis σA factor were constructed. B. subtilis DB1001 which contained an A197P substitution was very sensitive to temperature elevation. B. subtilis DB1002 had a T199G substitution and was low in growth potential at the elevated temperature. Degradation of σA in B. subtilis DB1001 (t1/2=63.2min) and DB1002 (t1/2=186.0min) occurred readily even at 37°C; however, σA in B. subtilis DB2 (wild-type) was fairly stable at the same temperature. The activities of both DB1001 and DB1002 σA factors on groE promoter (σA-type) were lower than those of the wild-type counterpart at both permissive and restrictive temperatures. The failure of a higher σA concentration to suppress the Ts phenotype of DB1001 indicated that the temperature sensitivity of B. subtilis DB1001 was due to altered function, rather than insufficient concentration, of σA in the cells. Taken together, our results suggest that the helicity of the promoter -10 binding helix is essential to the packing interaction in the hydrophobic core region of σA, which helps to maintain the stable and functional σA structure.
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