Provvedi R, Chen I, Dubnau D
Public Health Research Institute, 455 First Avenue, New York 10016, USA.
Mol Microbiol. 2001 May;40(3):634-44. doi: 10.1046/j.1365-2958.2001.02406.x.
We have re-examined the roles of nucA and nin, in the transformation of Bacillus subtilis as conflicting accounts have been presented concerning the importance of these genes for transformation. The present report demonstrates that nucA deficiency lowers the rate of DNA transport and that NucA is needed for the double-strand cleavage of transforming DNA, probably acting directly as an endonuclease. A relative paucity of DNA termini, resulting from the absence of this endonuclease activity, most probably accounts for the decreased transport rate. NucA is a bitopic integral membrane protein, with its C-terminus external to the membrane where it is appropriately located to effect the cleavage of bound transforming DNA. We have also investigated the roles of the known competence genes in the DNA processing that accompanies transformation in B. subtilis. The genes that are required for DNA transport (comEA, comEC and comFA) are also required for the degradation of the 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.
由于关于nucA和nin基因对枯草芽孢杆菌转化的重要性存在相互矛盾的说法，我们重新审视了它们在枯草芽孢杆菌转化过程中的作用。本报告表明，nucA缺陷会降低DNA转运速率，并且NucA是转化DNA双链切割所必需的，可能直接作为一种核酸内切酶发挥作用。由于缺乏这种核酸内切酶活性导致DNA末端相对较少，这很可能是转运速率降低的原因。NucA是一种双拓扑整合膜蛋白，其C末端位于膜外，在那里它的位置适当，能够对结合的转化DNA进行切割。我们还研究了已知的感受态基因在枯草芽孢杆菌转化过程中伴随的DNA加工中的作用。DNA转运所需的基因（comEA、comEC和comFA）对于内化过程中伴随的非转化链的降解也是必需的，但comEC和comFA对于细胞膜外发生的双链切割不是必需的。
