Studier F W, Movva N R
J Virol. 1976 Jul;19(1):136-45. doi: 10.1128/JVI.19.1.136-145.1976.
Deletion and point mutants of T3 have been isolated and used to show that the early region of T3 DNA is organized in the same way as that of T7 DNA. Homologous early RNAs and proteins of the two phages have been identified by electrophoresis on polyacrylamide gels in the presence of sodium dodecyl sulfate. Both phages have five early mRNA's, numbered 0.3, 0.7, 1,1.1 and 1.3 from left to right, although no T3 protein that corresponds to the 1.1 protein of T7 has yet been identified. In general, corresponding early RNAs and proteins of the two phages migrate differently on gels, indicating that they differ in molecular weight and/or conformation. In both T7 and T3, gene 0.3 is responsible for overcoming the DNA restriction system of the host, gene 0.7 specifies a protein kinase, gene 1 specifies a phage-specific RNA polymerase, and gene 1.3 specifies a polynucleotide ligase. The 0.3 protein of T3 is responsible for the S-adenosylmethionine cleaving activity (SAMase) induced after T3 (but not T7) infection. However, cleaving of S-adenosylmethionine does not appear to be the primary mechanism by which T3 overcomes host restriction, since at least one mutant of T3 has lost the SAMase activity without losing the ability to overcome host restriction.
T3的缺失突变体和点突变体已被分离出来，并用于证明T3 DNA的早期区域与T7 DNA的早期区域组织方式相同。通过在十二烷基硫酸钠存在下的聚丙烯酰胺凝胶电泳，已鉴定出两种噬菌体的同源早期RNA和蛋白质。两种噬菌体都有五种早期mRNA，从左到右编号为0.3、0.7、1、1.1和1.3，尽管尚未鉴定出与T7的1.1蛋白相对应的T3蛋白。一般来说，两种噬菌体相应的早期RNA和蛋白质在凝胶上的迁移方式不同，这表明它们在分子量和/或构象上存在差异。在T7和T3中，0.3基因负责克服宿主的DNA限制系统，0.7基因指定一种蛋白激酶，1基因指定一种噬菌体特异性RNA聚合酶，1.3基因指定一种多核苷酸连接酶。T3的0.3蛋白负责T3（而非T7）感染后诱导的S-腺苷甲硫氨酸裂解活性（SAMase）。然而，S-腺苷甲硫氨酸的裂解似乎不是T3克服宿主限制的主要机制，因为至少有一种T3突变体失去了SAMase活性，但没有失去克服宿主限制的能力。
