Host-specific activation of transcription by tandem repeats from simian virus 40 and Moloney murine sarcoma virus.

TLDR

SV40 72‑bp tandem repeats act as activators or enhancers of early viral transcription. The authors replaced SV40 repeats with MSV repeats in a recombinant genome and used a chloramphenicol acetyltransferase reporter assay to compare enhancer activity adjacent to the early SV40 promoter. In monkey kidney cells the recombinant virus replicates and expresses large tumor antigen more slowly than wild‑type SV40, whereas in mouse cells both viruses express similar antigen levels; reporter assays show SV40 repeats drive higher expression in monkey cells and MSV repeats in mouse cells, indicating host‑specific enhancer activity that may influence viral host range.

Abstract

The simian virus (SV40) 72-base pair (bp) tandem repeated sequences have recently been shown to function as activators or enhancers of early viral transcription. A recombinant viral genome was recently constructed by inserting 72-bp tandem repeats from the Moloney murine sarcoma virus (MSV) in place of the 72-bp repeats of SV40. Although this genome replicates in monkey kidney cells, its rate of large tumor antigen expression and replication is considerably slower than that of wild-type SV40. In mouse cells, however, equivalent levels of large tumor antigen appear to be expressed from both wild-type and recombinant genomes, suggesting a relationship between the level of enhancer activity and the host cell. To confirm this observation, we have applied a sensitive quantitative assay for gene expression based on the conversion of chloramphenicol to its acetylated forms. The gene encoding the enzymatic function chloramphenicol acetyltransferase was inserted into two vectors in which the enhancer sequences from SV40 or MSV were placed adjacent to the early SV40 promoter. The SV40 tandem repeats appear to activate gene expression to significantly higher levels in monkey kidney cells, but the MSV repeats are more active in two lines of mouse cells. These findings suggest that the tandem repeat elements may interact with host-specific molecules and, furthermore, may constitute one of the elements determining the host range of these eukaryotic viruses.