F- mating materials able to generate a mating signal in mating with HfrH dnaB(Ts) cells.

The purified outer membrane from F- (W1-3) cells was shown to inhibit mating effectively, but the purified cytoplasmic (inner) membrane did not. These membranes, heat-treated minicells, and ultraviolet-irradiated minicells were examined for their ability to generate a mating signal at 43 degrees C in mating with HfrH dnaB(Ts) cells. The outer and inner membranes and heat-treated minicells all failed to stimulate incorporation of radioactive thymine; only ultraviolet-irradiated minicells retained the ability to generate a mating signal for the donor to initiate transfer replication.