Leffers G G, Gottesman S
Laboratory of Molecular Biology, National Cancer Institute, Bethesda, Maryland 20892-4255, USA.
J Bacteriol. 1998 Mar;180(6):1573-7. doi: 10.1128/JB.180.6.1573-1577.1998.
Lambda Xis, which is required for site-specific excision of phage lambda from the bacterial chromosome, has a much shorter functional half-life than Int, which is required for both integration and excision (R. A. Weisberg and M. E. Gottesman, p. 489-500, in A. D. Hershey, ed., The Bacteriophage Lambda, 1971). We found that Xis is degraded in vivo by two ATP-dependent proteases, Lon and FtsH (HflB). Xis was stabilized two- to threefold more than in the wild type in a lon mutant and as much as sixfold more in a lon ftsH double mutant at the nonpermissive temperature for the ftsH mutation. Integration of lambda into the bacterial chromosome was delayed in the lon ftsH background, suggesting that accumulation of Xis in vivo interferes with integration. Overexpression of Xis in wild-type cells from a multicopy plasmid inhibited integration of lambda and promoted curing of established lysogens, confirming that accumulation of Xis interferes with the ability of Int to establish and maintain an integrated prophage.
λ噬菌体Xis蛋白是噬菌体λ从细菌染色体上进行位点特异性切除所必需的，其功能半衰期比整合和切除都需要的Int蛋白短得多（R. A. 韦斯伯格和M. E. 戈特斯曼，第489 - 500页，载于A. D. 赫希主编的《噬菌体λ》，1971年）。我们发现Xis蛋白在体内被两种ATP依赖的蛋白酶Lon和FtsH（HflB）降解。在ftsH突变的非允许温度下，Xis蛋白在lon突变体中比野生型稳定两到三倍，在lon ftsH双突变体中稳定多达六倍。在lon ftsH背景下，λ噬菌体整合到细菌染色体的过程延迟，这表明Xis蛋白在体内的积累会干扰整合。从多拷贝质粒在野生型细胞中过表达Xis蛋白会抑制λ噬菌体的整合并促进已建立的溶原菌的治愈，这证实了Xis蛋白的积累会干扰Int蛋白建立和维持整合原噬菌体的能力。
