Perez L, Wills J W, Hunter E
J Virol. 1987 Apr;61(4):1276-81. doi: 10.1128/JVI.61.4.1276-1281.1987.
Expression of the Rous sarcoma virus envelope gene (env) from a simian virus 40 (SV40) late-region replacement vector is dependent on the position of env within the SV40 late-region sequences. The difference in expression levels appeared to be due to differences in the efficiency with which the env-specific transcripts were translated, because transcription levels from different constructions were similar. Deletion of the nucleotides encoding the agnoprotein initiator codon, located upstream of the env sequences in the poorly expressed construct, resulted in high levels of env expression. The agnoprotein initiator codon and overlapping open reading frame thus act as strong barriers to further ribosome scanning and prevent initiation at the env AUG codon. We conclude that AUG codons present in the late region of SV40 can reduce expression of inserted genes positioned downstream. Nevertheless, intrinsic properties of the gene may determine its ultimate level of expression.
源自猿猴病毒40（SV40）晚期区域替换载体的劳氏肉瘤病毒包膜基因（env）的表达取决于env在SV40晚期区域序列中的位置。表达水平的差异似乎是由于env特异性转录本的翻译效率不同，因为不同构建体的转录水平相似。在低表达构建体中位于env序列上游的编码agnoprotein起始密码子的核苷酸缺失，导致env高水平表达。因此，agnoprotein起始密码子和重叠开放阅读框成为进一步核糖体扫描的强大障碍，并阻止在env AUG密码子处起始。我们得出结论，SV40晚期区域中存在的AUG密码子可降低下游插入基因的表达。然而，基因的内在特性可能决定其最终表达水平。
