ROUS-SARCOMA VIRUS-RNA STABILITY REQUIRES AN OPEN READING FRAME IN THE GAG GENE AND SEQUENCES DOWNSTREAM OF THE GAG-POL JUNCTION

The intracellular accumulation of the unspliced RNA of Rous sarcoma vi rus was decreased when translation was prematurely terminated by the i ntroduction of nonsense codons within its 5' proximal gene, the gag ge ne. Subcellular fractionation of transfected cells suggested that nons ense codon-mediated instability occurred in the cytoplasm. Analysis of constructs containing an in-frame deletion in the nucleocapsid domain of gag, which prevents interaction between the Gag protein and viral RNA, showed that an open reading frame extending to approximately 30 n ucleotides from the natural gag termination codon was needed for RNA s tability. Sequences at the gag-pol junction necessary for ribosomal fr ameshifting were not required for RNA stability; however, sequences lo cated 100 to 200 nucleotides downstream of the natural gag termination codon were found to be necessary for stable RNA. The stability of RNA s lacking this downstream sequence was not markedly affected by premat ure termination codons. We propose that this downstream RNA sequence m ay interact with ribosomes translating gag to stabilize the RNA.