FIG. 6.

Pulse-chase analysis of LexA cleavage for selected mutants. Derivatives of JL783 carrying pTrecA220 or mutant derivatives were grown as described in Materials and Methods; the strain marked ΔrecA carried pBR322. The cultures were treated with nalidixic acid for 30 min, followed by the addition of [³⁵S]methionine (50 μCi/ml) and sampling at the times indicated. The identity of each set of samples is indicated above the gel. The samples were precipitated with antibody to LexA and analyzed as described in the text. The locations of intact LexA and the C-terminal cleavage product are indicated. The other bands are cross-reacting species also precipitated by the antibody. In the ΔrecA strain, less LexA is made, because LexA negatively autoregulates its own expression.