Mechanism of transformation in B. subtilis

Summary

Transformation in B. subtilis is achieved by the uptake of donor DNA into recipient cells and the integration of part of this donor DNA into the host chromosome. The evidence presented in this report is interpreted to indicate that donor double helical DNA, on entry into host cells is rapidly membrane bound and can remain in this state for a consicerable time, perhaps even until integration. This bound DNA consists of molecules which have been reduced in size and degraded on uptake, and appear as partially single-stranded molecules. It is suggested that the donor DNA initially forms single strands which rapidly assume a partially single stranded nature by association with the host DNA or by reannealing.

Host cells, by virtue of the competent state, possess temporarily, and prior to the addition of donor DNA, chromosomes with single-stranded gaps. It is likely that such gaps are larger than the single-stranded segments of donor DNA which are to be integrated. Results are described which are best explained if integration is achieved by an initial annealing between the single-stranded donor and host segments followed by their covalent linkage.