Mutations in 3'-untranslated region of avian sarcoma virus mutant LA46 genome confer the cis-acting temperature-sensitive replication defect.

Avian sarcoma virus (ASV) PRCII mutant LA46 carried a unique cis-acting temperature sensitive (ts) defect affecting virus replication. The 3'-untranslated region of the LA46 genome contained multiple base substitutions in the direct repeat region and a long insertion. Although these sequences were not present in PRCII, most of these changes were found in various other ASVs and the long insertion shared extensive homology with the so called E region in certain ASV strains. By constructing chimeric retroviruses, the ts defect was mapped to the altered 3'-noncoding region. However, site-specific mutagenization targeted towards a four-nucleotide substitution unique to LA46 failed to implicate these mutations in the ts phenotype.