Karnik S, Billeter M
Institut für Molekularbiologie I, Universität Zürich, Switzerland.
EMBO J. 1983;2(9):1521-6. doi: 10.1002/j.1460-2075.1983.tb01617.x.
Complete or partial cDNA sequences of the RNA bacteriophage Qbeta were cloned in plasmids under the control of the lambdaP(L) promoter to allow regulated expression in Escherichia coli harbouring the gene for the temperature-sensitive lambdaCI857 repressor. Induction of the complete Qbeta sequence leads to a 100-fold increase in phage production, accompanied by cell lysis. Induction of the 5'-terminal sequence containing the intact maturation protein (A2) cistron also causes cell lysis. Alterations of the A2 cistron, leading to proteins either devoid of approximately 20% of the C-terminal region or of six internal amino acids, abolish the lysis function. Expression of other cistrons in addition to the A2 cistron does not enhance host lysis. Thus, in Qbeta, the A2 protein, in addition to its functions as maturation protein, appears to trigger cell lysis. This contrasts with the situation in the distantly related group I RNA phages such as f2 and MS2 where a small lysis polypeptide is coded for by a region overlapping the end of the coat gene and the beginning of the replicase gene.
RNA噬菌体Qβ的完整或部分cDNA序列被克隆到受λP(L)启动子控制的质粒中，以便在携带温度敏感型λCI857阻遏物基因的大肠杆菌中进行调控表达。诱导完整的Qβ序列会导致噬菌体产量增加100倍，并伴随细胞裂解。诱导包含完整成熟蛋白（A2）顺反子的5'-末端序列也会导致细胞裂解。A2顺反子的改变导致蛋白质缺失大约20%的C末端区域或六个内部氨基酸，从而消除裂解功能。除A2顺反子外，其他顺反子的表达不会增强宿主裂解。因此，在Qβ中，A2蛋白除了作为成熟蛋白发挥功能外，似乎还会触发细胞裂解。这与远缘的I组RNA噬菌体（如f2和MS2）的情况形成对比，在这些噬菌体中，一个小的裂解多肽由与外壳基因末端和复制酶基因起始部分重叠的区域编码。
