Activation of cryptic splice sites in murine sarcoma virus-124 mutants.
We have examined splice site activation in relation to intron structure in murine sarcoma virus (MuSV)-124 RNA. MuSV-124 contains inactive murine leukemia virus env gene splice sites (termed 5' env and 3' env) as well as cryptic sites in the gag and v-mos genes (termed 5' gag and 3' mos) which are activated for thermosensitive splicing by a 1,487-base intronic deletion in the MuSV-124 derived MuSVts110 retrovirus. To determine conditions permissive for splice site activation, we examined MuSV-124 mutants deleted in the 1,919-base intron bounded by the 5' gag and 3' mos sites. Several of these deletions activated thermosensitive splicing either at the same sites used in MuSVts110 or in a previously unreported temperature-sensitive splice event between the 5' gag and 3' env sites. These data suggested that the thermosensitive splicing phenotype characteristic of MuSVts110 required neither a specialized intron nor selection of a particular 3' splice site. The 3' env and 3' mos sites were found to compete for splicing to the 5' gag site; the more upstream 3' env site was exclusively used in MuSV-124 mutants containing both sites, whereas selection of the 3' mos site required removal of the 3' env site. Branchpoint sequences were found to have a potential regulatory role in thermosensitive splicing. Insertion of a beta-globin branchpoint sequence in a splicing-inactive MuSV-124 mutant activated efficient nonthermosensitive splicing at the 3' mos site, whereas a mutated branchpoint activated less efficient but thermosensitive splicing.
de Mars
M
M
Department of Tumor Biology, University of Texas M.D. Anderson Cancer Center, Houston 77030.
Cizdziel
P E
PE
Murphy
E C
EC
D001483:Base Sequence; D004252:DNA Mutational Analysis; D015752:Genes, env; D007438:Introns; D008969:Molecular Sequence Data; D009154:Mutation; D012326:RNA Splicing; D012367:RNA, Viral / Q000235:genetics*; D012045:Regulatory Sequences, Nucleic Acid; D009053:Sarcoma Viruses, Murine / Q000235:genetics*; D013696:Temperature
D012367:RNA, Viral