Bronson M J, Levine M
J Virol. 1971 May;7(5):559-68. doi: 10.1128/JVI.7.5.559-568.1971.
Mutants of phage P22 which form plaques on a P22 lysogen have been isolated. These virulent mutants have been classified into three groups. (i) VirA mutants arise spontaneously in wild-type stocks and form very small turbid plaques on a P22 lysogen. The single mutation responsible for VirA virulence maps near the mnt locus, one of the immunity regions of phage P22. (ii) VirB mutants do not arise spontaneously and have been isolated only from mutagenized P22 stocks. VirB mutants form small, clear plaques on a P22 lysogen. One of the VirB mutants, virB-3, was analyzed in detail. The virB-3 mutant is comprised of two mutations: K5, which maps within the c(2) gene, and Vx, which maps in the region between the c(2) and c(3) genes. Phages carrying either the K5 or Vx mutation are not virulent in themselves but mutate to VirB virulence at a frequency of 10(-5) to 10(-6). It is concluded that K5 and Vx are mutations at specific sites which together confer the ability to undergo phage development in the presence of repressor. (iii) VirC mutants are defined by a large clear plaque morphology when plated on a P22 lysogen. VirC mutants are comprised of the determinants of both VirA and VirB virulence.
已分离出能在P22溶原菌上形成噬菌斑的噬菌体P22突变体。这些烈性突变体已被分为三组。（i）VirA突变体在野生型菌系中自发产生，在P22溶原菌上形成非常小的浑浊噬菌斑。导致VirA烈性的单一突变定位在mnt基因座附近，mnt基因座是噬菌体P22的免疫区域之一。（ii）VirB突变体不会自发产生，仅从诱变的P22菌系中分离得到。VirB突变体在P22溶原菌上形成小的清晰噬菌斑。对其中一个VirB突变体virB - 3进行了详细分析。virB - 3突变体由两个突变组成：K5，定位在c(2)基因内；Vx，定位在c(2)和c(3)基因之间的区域。携带K5或Vx突变的噬菌体本身不具有烈性，但会以10^(-5)至10^(-6)的频率突变为VirB烈性。得出的结论是，K5和Vx是特定位点的突变，二者共同赋予了在存在阻遏物的情况下进行噬菌体发育的能力。（iii）VirC突变体在接种到P22溶原菌上时表现为大的清晰噬菌斑形态。VirC突变体由VirA和VirB烈性的决定因素组成。
