The Importance of Region 2.1 in Sustaining the Functional Structure of the Bacillus subtilis σ^A Factor

抄録

Region 2.1 of the σ factor is once proposed to be involved in core binding, and certain bulky hydrophobic amino acids in region 2.1 are thought to make contact with the conserved isoleucine residues in the promoter -10 binding region on the same protein. To examine the roles of the contact between these two regions in σ^A structure and function, σ^A factor with L145A, I149A, or Y153A was created, and the effects of each substitution on the growth of Bacillus subtilis and on the structural and functional properties of σ^A were analyzed. Our data revealed that the growth potential of B. subtilis was signifi-cantly affected by each of the substitutions of σ^A at elevated temperature. The growth defect was most pronounced with the strain containing L145A-σ^A; it possessed a low growth potential even at 37°C. In parallel, changes in the structural stability and corebinding activity of at and in the promoter-binding and transcription activities of σ^A-RNA polymerase were observed for each of the substitutions, with the most drastic effects exerted by L145A. Clearly, region 2.1 of σ^A has extra functions, such as the binding of RNA polymerase to promoter DNA, other than the known core-binding ability. Moreover, the multiple effects of each of the substitutions on crA demonstrate that the contacts between the hydrophobic amino acids in region 2.1 and those in the promoter -10 binding region are critical to the maintenance of the functional o-A structure and that L 145 in region 2.1 plays an important role in this respect.