NucA is required for DNA cleavage during transformation of Bacillus subtilis

We have re-examined the roles of nucA and nin, in the transformation of Bac illus subtilis as conflicting accounts have been presented concerning the i mportance of these genes for transformation. The present report demonstrate s that nucA deficiency lowers the rate of DNA transport and that NucA is ne eded for the double-strand cleavage of transforming DNA, probably acting di rectly as an endonuclease. A relative paucity of DNA termini, resulting fro m the absence of this endonuclease activity, most probably accounts for the decreased transport rate. NucA is a bitopic integral membrane protein, wit h its C-terminus external to the membrane where it is appropriately located to effect the cleavage of bound transforming DNA. We have also investigate d the roles of the known competence genes in the DNA processing that accomp anies transformation in B. subtilis. The genes that are required for DNA tr ansport (comEA, comEC and comFA) are also required for the degradation of t he non-transforming strand that accompanies internalization, but comEC and comFA are not needed for the double-strand cleavage that occurs external to the cell membrane.