期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1992
卷号：89
期号：2
页码：713-717
DOI：10.1073/pnas.89.2.713
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Synthesis of the pol gene products of most retroviruses requires ribosomes to shift frame once or twice in the -1 direction while translating gag-pol mRNA. The viral signals for frameshifting include a heptanucleotide sequence on which the shift occurs and higher-order RNA structure just downstream of the shift site. We have made site-directed mutations in two stems (S1 and S2) of a putative RNA pseudoknot that begins 7 nucleotides 3' of the previously identified shift site (A AAA AAC) in the gag-pro region of mouse mammary tumor virus (MMTV) RNA. The mutants confirm the predicted structure, show that loss of either S1 or S2 impairs frameshifting, and exclude alternative RNA structures as significant for frameshifting. The importance of the MMTV pseudoknot has been further demonstrated by showing that shift sites from two other retroviruses function more efficiently in the position of the MMTV site than in their native contexts. However, the MMTV pseudoknot cannot promote detectable frameshifting in the absence of a recognizable upstream shift site. In addition, the species of tRNA that reads the second codon in the shift site appears to be a critical determinant, since changing the 7th nucleotide in the MMTV gag-pro shift site from C to A, U, or G severely impairs frameshifting.
