title: Methylation of the promoter for an immediate-early frog virus 3 gene does not inhibit transcription.
abstract: Methylation of critical sites within the promoter region of eucaryotic genes has been shown to inhibit transcription by RNA polymerase II. However, although the large DNA virus frog virus 3 (FV3) has a highly methylated genome, it uses host RNA polymerase II for at least the immediate-early stage of transcription. We have previously shown that an FV3-induced trans-acting protein allows transcription from adenovirus promoters inactivated by methylation. Since FV3 immediate-early genes are transcribed in the absence of de novo protein synthesis, it appears that the virus-induced trans-acting protein that allows transcription from methylated templates is not required for transcription of the immediate-early FV3 genes, possibly because they are not methylated in critical regulatory sequences. In this study, we used site-directed mutagenesis to alter the three CpG dinucleotide sequences in the promoter region of an immediate-early FV3 gene and thereby created sites recognized by bacterial methylases. Transient-expression assays demonstrated that neither the mutations nor methylation of the mutated sites inhibited transcription from the FV3 promoter in FV3-infected cells. These findings support the hypothesis that the immediate-early genes of FV3 do not contain methylatable sites in regions critical for transcription. The function of the virus-induced trans-acting protein that can override the inhibitory effect of methylation may therefore be to facilitate the transcription of methylated delayed-early or late FV3 genes.
authors.affiliation: Department of Virology and Molecular Biology, St. Jude Children's Research Hospital, Memphis, Tennessee 38101-0318.
authors.forename: J P
authors.initials: JP
authors.lastname: Thompson
authors.forename: A
authors.initials: A
authors.lastname: Granoff
authors.forename: D B
authors.initials: DB
authors.lastname: Willis
mesh_terms: D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D004262:DNA Restriction Enzymes; D004279:DNA, Viral / Q000235:genetics / Q000378:metabolism*; D007497:Iridoviridae / Q000235:genetics*; D008745:Methylation; D008969:Molecular Sequence Data; D009154:Mutation; D011401:Promoter Regions, Genetic; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D004279:DNA, Viral; D004262:DNA Restriction Enzymes