Haijema B J, Venema G, Kooistra J
Department of Genetics, Biomolecular Sciences and Biotechnology Institute, University of Groningen, The Netherlands.
J Bacteriol. 1996 Sep;178(17):5086-91. doi: 10.1128/jb.178.17.5086-5091.1996.
Comparison of subunit AddA of the Bacillus subtilis AddAB enzyme, subunit RecB of the Escherichia coli RecBCD enzyme, and subunit RecB of the Haemophilus influenzae RecBCD enzyme revealed several regions of homology. Whereas the first seven regions are common among helicases, the two C-terminally located regions are unique for RecB of E. coli and H. influenzae and AddA. Deletion of the C-terminal region resulted in the production of an enzyme which showed moderately impaired levels of ATP-dependent helicase activity, whereas the ATP-dependent exonuclease activity was completely destroyed. The mutant enzyme was almost completely capable of complementing E. coli recBCD and B. subtilis addAB strains with respect to DNA repair and homologous recombination. These results strongly suggest that at least part of the C-terminal region of the AddA protein is indispensable for exonuclease activity and that, in contrast to the exonuclease activity, the helicase activity of the addAB gene product is important for DNA repair and homologous recombination.
对枯草芽孢杆菌AddAB酶的亚基AddA、大肠杆菌RecBCD酶的亚基RecB以及流感嗜血杆菌RecBCD酶的亚基RecB进行比较，发现了几个同源区域。前七个区域在解旋酶中是常见的，而位于C末端的两个区域是大肠杆菌和流感嗜血杆菌的RecB以及AddA所特有的。C末端区域的缺失导致产生一种酶，该酶的ATP依赖性解旋酶活性水平中度受损，而ATP依赖性核酸外切酶活性则完全被破坏。突变酶在DNA修复和同源重组方面几乎完全能够互补大肠杆菌recBCD和枯草芽孢杆菌addAB菌株。这些结果强烈表明，AddA蛋白C末端区域的至少一部分对于核酸外切酶活性是不可或缺的，并且与核酸外切酶活性相反，addAB基因产物的解旋酶活性对于DNA修复和同源重组很重要。
