Tesar M, Marquardt O
Federal Research Center of Virus Diseases of Animals, Tübingen, Federal Republic of Germany.
Virology. 1990 Feb;174(2):364-74. doi: 10.1016/0042-6822(90)90090-e.
Foot-and-mouth disease virus protease 3C is essential for the processing of the viral precursor polyprotein. It is shown here to also inhibit gene expression in baby hamster kidney cells after transient expression from transfected cDNA fragments. Protease 3C could not be detected by indirect immunofluorescence in contrast to other cDNA-encoded virus proteins, but protein synthesized de novo 16 hr after transfection could be detected by radioimmunoprecipitation. The cellular translation apparatus was, therefore, not inhibited. The enzyme, although produced as part of a fusion protein, was in size indistinguishable from that found in virus-infected cells. This suggested that the enzyme was released by autocatalysis from the recombinant fusion protein and from viral precursor protein in a similar manner. Transcription of protease 3C-encoding cDNA fragments as well as that of cotransfected fragments, which do not encode protease 3C, was inhibited as determined by hybridization assays. The shut off of transcription which was one of the cytopathic effects observed in virus-infected cells therefore correlates with the production of transactive protease 3C. The inhibitory molecular mechanism may involve truncation of the nuclear protein histone H3 at its N-terminus since this protein was found similarly truncated in virus-infected cells and after transfer of 3C-encoding cDNA fragments.
口蹄疫病毒蛋白酶3C对于病毒前体多聚蛋白的加工至关重要。本文显示，从转染的cDNA片段瞬时表达后，它在幼仓鼠肾细胞中也能抑制基因表达。与其他cDNA编码的病毒蛋白不同，间接免疫荧光法检测不到蛋白酶3C，但转染16小时后新合成的蛋白可通过放射免疫沉淀法检测到。因此，细胞翻译装置未受抑制。该酶虽然作为融合蛋白的一部分产生，但其大小与在病毒感染细胞中发现的酶无法区分。这表明该酶以类似方式通过自催化从重组融合蛋白和病毒前体蛋白中释放出来。通过杂交分析确定，编码蛋白酶3C的cDNA片段以及共转染的不编码蛋白酶3C的片段的转录均受到抑制。因此，在病毒感染细胞中观察到的细胞病变效应之一——转录关闭，与具有反式激活作用的蛋白酶3C的产生相关。抑制性分子机制可能涉及核蛋白组蛋白H3在其N端的截短，因为在病毒感染细胞以及转染编码3C的cDNA片段后，都发现该蛋白有类似的截短。
