FIG 1.

Hypothetical functions of ComW as a σ factor adapter or in sequestration of σ^A during competence in S. pneumoniae. Two main mechanisms are suggested for ComW's mode of action during transformation, blocking σ^A association with E (core RNA polymerase) or promoting σ^X association with core RNAP. However, many steps exist with either mechanism, and ComW could act at any of these steps. For example, if the role of ComW is to prevent σ^A association with core RNAP, it might act by sequestering σ^A (?₁) or by preventing σ^A from accessing core RNAP (?₂). If ComW acts to increase σ^X access to core RNAP, it might act by directly binding σ^X (?₃) or by promoting the loading of σ^X onto core RNAP (?₄). It could also act to promote switching between the two sigma factors (?₅). Purple squares, ComW; beige circles, σ^A; magenta circles, σ^X; gray ovals, core RNA polymerase; green pentagon, housekeeping genes; brown and orange pentagons, late genes; ?, hypothetical locations of ComW action; boxed c's, cin-boxes.