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

The genomes of all replication-competent retroviruses contain cis-acting el ements that regulate gene expression. However, the identities of many of th ese elements remain to be characterized. Inserting sequences into the 3' un translated region of a replication-competent spleen necrosis virus (SNV) ve ctor disrupted its ability to replicate. Inserts varying in sequences and s izes (0.4-kb to 1.6-kb) all resulted in this defect. Genetic compensation e xperiments and immunostaining revealed that env gene expression was deficie nt. Northern analysis indicated the presence of spliced viral mRNA of the c orrect size although at a reduced level compared to a wildtype vector. It i s likely that the block in env expression occurs at a post-transcriptional step. These results suggest that the function of a cis-acting element disti nct from the constitutive transport element is disrupted by the inserted se quences into the 3' untranslated region of SNV.