Department of Biological Sciences, University at Buffalo, Buffalo, NY 14260, USA.
Viruses. 2013 Jan 9;5(1):111-26. doi: 10.3390/v5010111.
In a λ(imm434) lysogen, two proteins are expressed from the integrated prophage. Both are encoded by the same mRNA whose transcription initiates at the P(RM) promoter. One protein is the 434 repressor, needed for the establishment and maintenance of lysogeny. The other is Hex which is translated from an open reading frame that apparently partially overlaps the 434 repressor coding region. In the wild type host, disruption of the gene encoding Hex destabilizes λ(imm434) lysogens. However, the hex mutation has no effect on lysogen stability in a recA(-) host. These observations suggest that Hex functions by modulating the ability of RecA to stimulate 434 repressor autocleavage. We tested this hypothesis by identifying and purifying Hex to determine if this protein inhibited RecA‑stimulated autocleavage of 434 repressor in vitro. Our results show that in vitro a fragment of Hex prevents RecA-stimulated autocleavage of 434 repressor, as well as the repressors of the closely related phage P22. Surprisingly, Hex does not prevent RecA‑stimulated autocleavage of phage lambda repressor, nor the E. coli LexA repressor.
在 λ(imm434)溶源菌中，两种蛋白质由整合的噬菌体表达。这两种蛋白质都是由同一个 mRNA 编码的，其转录起始于 P(RM)启动子。一种蛋白质是 434 阻遏物，它是建立和维持溶源性所必需的。另一种是 Hex，它是从一个开放阅读框翻译而来的，该阅读框显然部分重叠了 434 阻遏物的编码区。在野生型宿主中，编码 Hex 的基因的破坏会使 λ(imm434)溶源菌不稳定。然而，在 recA(-)宿主中，hex 突变对溶源菌的稳定性没有影响。这些观察结果表明，Hex 通过调节 RecA 刺激 434 阻遏物自身切割的能力来发挥作用。我们通过鉴定和纯化 Hex 来验证这一假设，以确定该蛋白是否在体外抑制 RecA 刺激的 434 阻遏物自身切割。我们的结果表明，在体外，Hex 的一个片段可阻止 RecA 刺激的 434 阻遏物自身切割，以及与噬菌体 P22 密切相关的噬菌体的阻遏物自身切割。令人惊讶的是，Hex 不会阻止 RecA 刺激的噬菌体 lambda 阻遏物或大肠杆菌 LexA 阻遏物的自身切割。
