Transformation of Bacillus subtilis competent cells: identification of a protein involved in recombination.

With the use of two-dimensional gel electrophoresis, the proteins present in a transformation-proficient B. subtilis strain were compared with those present in an isogenic, recombination-deficient strain carrying the recE4 mutation. One protein (molecular weight 45 kD, iso-electric point 5.4) was found to be virtually absent in the recE4 strain. This 45 kD protein is a prominent protein predominantly present in the competent fraction of a competent culture. The synthesis of the protein is substantially stimulated by irradiation with ultraviolet light or treatment with mitomycin C and, to a lesser extent, by treatment with nalidixic acid. Since the protein is also observed in a strain cured for SP beta and carrying non-inducible PBS X, it is unlikely that this protein is a gene product specified by one of these prophages usually present in B. subtilis strain 168. Based on these results we conclude that the 45 kD protein is involved in recombination in B. subtilis.