Degnin C R, Schleiss M R, Cao J, Geballe A P
Department of Molecular Medicine, Fred Hutchinson Cancer Research Center C2-023, Seattle, Washington 98104-2092.
J Virol. 1993 Sep;67(9):5514-21. doi: 10.1128/JVI.67.9.5514-5521.1993.
The human cytomegalovirus (CMV) virion glycoprotein gpUL4 (gp48) gene expresses a transcript that contains three AUG codons upstream from the one used to initiate synthesis of the gp48 protein. Previously we reported that the second of these AUG codons, AUG2, was necessary but insufficient for inhibition of downstream translation (M. Schleiss, C. R. Degnin, and A. P. Geballe, J. Virol. 65:6782-6789, 1991). We now demonstrate that the coding information of the upstream open reading frame initiated by AUG2 (uORF2) is critical for the inhibitory signal. Several missense mutations, particularly those involving the carboxy-terminal codons of uORF2, inactivate the inhibitory signal, while mutations that preserve the coding content of uORF2 uniformly retain the inhibitory signal. The uORF2 termination codon is essential for inhibition, but leader sequences further downstream are not critical. Conservation of uORF2 among clinical strains of CMV suggests that uORF2 provides an important function in the CMV infectious cycle. Although these results indicate that the peptide product of uORF2 mediates the inhibitory effect, we demonstrate that the uORF2 signal acts only in cis, and we propose a model of inhibition by the gp48 uORF2 signal.
人类巨细胞病毒（CMV）病毒体糖蛋白gpUL4（gp48）基因表达一种转录本，该转录本在用于起始gp48蛋白合成的AUG密码子上游含有三个AUG密码子。此前我们报道，这些AUG密码子中的第二个，即AUG2，对于抑制下游翻译是必要的，但并不充分（M. Schleiss、C. R. Degnin和A. P. Geballe，《病毒学杂志》65:6782 - 6789，1991）。我们现在证明，由AUG2起始的上游开放阅读框（uORF2）的编码信息对于抑制信号至关重要。几个错义突变，特别是那些涉及uORF2羧基末端密码子的突变，会使抑制信号失活，而保留uORF2编码内容的突变则一致地保留了抑制信号。uORF2终止密码子对于抑制是必不可少的，但更下游的前导序列并不关键。CMV临床菌株中uORF2的保守性表明uORF2在CMV感染周期中发挥重要作用。虽然这些结果表明uORF2的肽产物介导了抑制作用，但我们证明uORF2信号仅顺式作用，并且我们提出了一个由gp48 uORF2信号介导的抑制模型。
