Tumorigenic poxviruses: characterization of the expression of an epidermal growth factor related gene in Shope fibroma virus.

The transcription and translation of an epidermal growth factor (EGF) related gene in the Leporipoxvirus Shope fibroma virus (SFV), termed the Shope fibroma growth factor (SFGF), have been characterized. Three early RNA transcripts complimentary to an anti-SFGF oligonucleotide were detected by Northern blot analysis, while no late transcripts were expressed. The activity of the SFGF early promoter was measured using a transient gene expression assay in SFV-infected cells using the bacterial choloramphenicol acetyltransferase as a reporter gene. Deletion analysis showed that the functional SFGF promoter domain is an AT-rich sequence contained within 30 bp of the major transcriptional initiation site as is typical of early poxvirus promoters. An intracellular form of the SFGF gene product was immunoprecipitated from infected lysates using rabbit antisera raised against a synthetic SFGF (amino acids 26-80). A 16-kDa product was detected, while in cells infected in the presence of tunicamycin, the immunoprecipitated product had a mobility on SDS-polyacrylamide gels of approximately 6 kDa, indicating that the SFGF gene product is extensively post-transcriptionally modified. The intracellular 16-kDa form can be pulse-chased to a 14-kDa form but the secreted form of SFGF could not be detected in the medium using this anti-peptide antiserum.