Morton D, Kutter E M, Guttman B S
J Virol. 1978 Oct;28(1):262-9. doi: 10.1128/JVI.28.1.262-269.1978.
Several lines of research have suggested that the dCMP hydroxymethylase (HMase) coded by bacteriophage T4 is an essential protein in a DNA replication complex, as well as a supplier of hydroxymethyl dCMP for phage DNA synthesis. We show that a mutant [HMase, dCTPase, endonuclease II, endonuclease IV] which lacked this enzyme made cytosine-containing DNA at about two-thirds of the normal rate. When coupled with an alc mutation which permitted synthesis of late proteins, a small burst of phage was produced whose DNA contained no hydroxymethylcytosine. This pentuple mutant made both early and late proteins with abnormal kinetics, whereas the HMase+ parent showed normal kinetics. However, intracellular phage DNA showed no gross abnormalities in alkaline sucrose gradients. We conclude that HMase is not required for DNA synthesis when hydroxymethyl dCMP is not needed as a substrate; however, its absence still impairs both replication and transcription.
多项研究表明，噬菌体T4编码的dCMP羟甲基化酶（HMase）是DNA复制复合物中的一种必需蛋白质，也是噬菌体DNA合成中羟甲基dCMP的供应者。我们发现，一个缺乏这种酶的突变体[HMase、dCTPase、核酸内切酶II、核酸内切酶IV]以大约正常速率的三分之二合成含胞嘧啶的DNA。当与允许晚期蛋白质合成的alc突变相结合时，会产生一小批噬菌体，其DNA不含羟甲基胞嘧啶。这个五重突变体合成早期和晚期蛋白质的动力学异常，而HMase+亲本表现出正常的动力学。然而，细胞内噬菌体DNA在碱性蔗糖梯度中未显示出明显异常。我们得出结论，当不需要羟甲基dCMP作为底物时，DNA合成不需要HMase；然而，它的缺失仍然会损害复制和转录。
