Expression from an internal AUG codon of herpes simplex thymidine kinase gene inserted in a retrovirus vector

We identified structural features that affect the expression of an exogenous gene inserted into a retrovirus vector constructed by using spleen necrosis virus, an avian retrovirus. The thymidine kinase gene from herpes simplex virus type 1 containing deletions in the promoter and terminal sequences of the mRNA was inserted into spleen necrosis virus. We found that synthesis of thymidine kinase by the recovered virus was apparently initiated from internal AUG residues. At least in some cases, however, the level of expression depended on the number of AUGs and the nucleotide sequence around the AUGs that preceded the initiator codon of the thymidine kinase gene.