Insertion of sequences into the 3′ untranslated region of a replication-competent spleen necrosis virus vector disrupts env gene expression

Summary

The genomes of all replication-competent retroviruses contain cis-acting elements that regulate gene expression. However, the identities of many of these elements remain to be characterized. Inserting sequences into the 3′ untranslated region of a replication-competent spleen necrosis virus (SNV) vector disrupted its ability to replicate. Inserts varying in sequences and sizes (0.4-kb to 1.6-kb) all resulted in this defect. Genetic compensation experiments and immunostaining revealed that env gene expression was deficient. Northern analysis indicated the presence of spliced viral mRNA of the correct size although at a reduced level compared to a wildtype vector. It is likely that the block in env expression occurs at a post-transcriptional step. These results suggest that the function of a cis-acting element distinct from the constitutive transport element is disrupted by the inserted sequences into the 3′ untranslated region of SNV.