Meyer T F, Geider K
J Biol Chem. 1979 Dec 25;254(24):12642-6.
Bacteriophage fd gene II-protein was characterized as an endonuclease which specifically nicked supercoiled replicative form (RF) of filamentous phages in the viral strand. No other supercoiled DNAs tested were attacked by the enzyme, nor were doubly closed fd RF in the relaxed state nor phage fd single strands. Maximal activity was found at pH 8.5 and 80 mM KCl using fd RFI of physiological superhelicity. Mg2+, but no other cofactor, was required for the cleavage reaction. A sealing activity was found to be associated with the enzyme. At a higher concentration of Mg2+ up to 40% of the reaction products were found as doubly closed relaxed fd RF. The protein was not found to be tightly attached to the cleaved strand.
噬菌体fd基因II蛋白被鉴定为一种核酸内切酶，它能特异性地在病毒链上切割丝状噬菌体的超螺旋复制型（RF）。测试的其他超螺旋DNA均未被该酶攻击，处于松弛状态的双链闭合fd RF以及噬菌体fd单链也未被攻击。使用具有生理超螺旋度的fd RFI，在pH 8.5和80 mM KCl条件下发现最大活性。切割反应需要Mg2+，但不需要其他辅因子。发现该酶具有封闭活性。在较高浓度的Mg2+条件下，高达40%的反应产物为双链闭合的松弛fd RF。未发现该蛋白与切割链紧密结合。
