Reexamination of phenotypic defects in rec-1 and rec-2 mutants of Haemophilus influenzae Rd

Radiolabeled donor DNA is efficiently taken up into competent H. influenzae Rd rec-2 mutant cells but does not undergo the rapid degradation observed in wild-type cells, and donor label is not recovered in the chromosome even after 1 h, interpreted as a failure of the donor DNA to be translocated out of the transformasome.

Abstract

Radiolabeled donor DNA is efficiently taken up into competent H. influenzae Rd rec-2 mutant cells but does not undergo the rapid degradation observed in wild-type cells. Furthermore, donor label is not recovered in the chromosome even after 1 h. The donor DNA appears to remain in a protected state in a compartment that can be separated from the rest of the cell. We interpret this as a failure of the donor DNA to be translocated out of the transformasome. In contrast, rec-1 cells translocate labeled donor DNA normally. The donor label accumulates in the recipient chromosome, but, as expected for cells with a recombination defect, there is no preferential localization of the label in sites homologous to the donor DNA. In addition, we have observed two enzymatic activities that act on transformasome-associated DNA of rec-2 cells, an endonuclease which may play a role in the translocation of closed circular DNA and a phosphatase.