Differential expression of two immediate early genes of herpesvirus saimiri as detected by in situ hybridization.

Transcripts from two immediate early (IE) genes have been identified in cells infected with the gamma herpesvirus, herpesvirus saimiri. One is a 1.3 kb RNA transcribed from the HindIII-G fragment of virus DNA (IE-G), the other is a 1.6 kb RNA from the gene for the IE 52K phosphoprotein. Labelled oligonucleotide probes specific for each of these RNAs have been used in in situ hybridization experiments to compare their expression in individual cells in infected populations. In the presence of cycloheximide, the IE-G RNA accumulates synchronously throughout the population of infected cells and prior to the asynchronous accumulation of RNA from the gene for the IE 52K protein in the same population of cells. This heterogeneity in the timing of expression of RNA from the IE 52K gene is paralleled by the asynchronous accumulation of the protein product. We conclude that transcription of the IE-G RNA is independent of expression of the IE 52K gene and that expression of the 52K gene requires (or is prevented by) factors which do not affect accumulation of the RNA from the IE-G gene.