Pekosz A, Lamb R A
Howard Hughes Medical Institute, Molecular Biology, and Cell Biology, Northwestern University, Evanston, IL 60208-3500, USA.
Proc Natl Acad Sci U S A. 1998 Oct 27;95(22):13233-8. doi: 10.1073/pnas.95.22.13233.
The influenza C virus CM2 protein is a small glycosylated integral membrane protein (115 residues) that spans the membrane once and contains a cleavable signal sequence at its N terminus. The coding region for CM2 (CM2 ORF) is located at the C terminus of the 342-amino acid (aa) ORF of a colinear mRNA transcript derived from influenza C virus RNA segment 6. Splicing of the colinear transcript introduces a translational stop codon into the ORF and the spliced mRNA encodes the viral matrix protein (CM1) (242 aa). The mechanism of CM2 translation was investigated by using in vitro and in vivo translation of RNA transcripts. It was found that the colinear mRNA derived from influenza C virus RNA segment 6 serves as the mRNA for CM2. Furthermore, CM2 translation does not depend on any of the three in-frame methionine residues located at the beginning of CM2 ORF. Rather, CM2 is a proteolytic cleavage product of the p42 protein product encoded by the colinear mRNA: a cleavage event that involves the recognition and cleavage of an internal signal peptide presumably by signal peptidase resident in the endoplasmic reticulum. Alteration of the predicted signal peptidase cleavage site by mutagenesis blocked generation of CM2. The other polypeptide species resulting from the cleavage of p42, designated p31, contains the CM1 coding region and an additional C-terminal 17 aa (formerly the CM2 signal peptide). Protein p31, in comparison to CM1, displays characteristics of an integral membrane protein.
丙型流感病毒CM2蛋白是一种小的糖基化整合膜蛋白（115个氨基酸残基），它跨膜一次，在其N端含有一个可裂解的信号序列。CM2的编码区（CM2开放阅读框）位于源自丙型流感病毒RNA片段6的共线性mRNA转录本的342个氨基酸（aa）开放阅读框的C端。共线性转录本的剪接在开放阅读框中引入了一个翻译终止密码子，剪接后的mRNA编码病毒基质蛋白（CM1）（242个aa）。通过对RNA转录本进行体外和体内翻译来研究CM2的翻译机制。发现源自丙型流感病毒RNA片段6的共线性mRNA作为CM2的mRNA。此外，CM2的翻译不依赖于位于CM2开放阅读框起始处的三个框内甲硫氨酸残基中的任何一个。相反，CM2是由共线性mRNA编码的p42蛋白产物的蛋白水解切割产物：这一切割事件可能涉及内质网中驻留的信号肽酶对内部信号肽的识别和切割。通过诱变改变预测的信号肽酶切割位点会阻止CM2的产生。由p42切割产生的另一种多肽产物，称为p31，包含CM1编码区和额外的C端17个aa（以前是CM2信号肽）。与CM1相比，蛋白p31表现出整合膜蛋白的特征。
