Regulation of alpha genes of herpes simplex virus: the alpha 27 gene promoter-thymidine kinase chimera is positively regulated in converted L cells.

In cells infected with herpes simplex virus 1, the expression of viral genes is coordinately regulated and sequentially ordered; the alpha genes are expressed first and are followed by beta and gamma genes in a cascade fashion. Earlier, this laboratory reported (Post et al., Cell 24:555-565, 1981) that a chimeric gene, constructed by the replacement of 50 base pairs of DNA coding for 5' nontranslated leader and sequences upstream of the site of transcription initiation of thymidine kinase (a beta gene) by corresponding sequences of alpha gene no. 4, was regulated as an alpha gene. Of particular interest was the observation that in cells converted to TK(+) phenotype, the chimeric gene was positively regulated by superinfecting virus. In this paper, we report two series of experiments. First, we determined that transcription of alpha gene no. 27 is initiated at or near a five-nucleotide sequence flanked by an eight-nucleotide perfect inverted repeat situated from 256 to 277 bases to the right of the left terminus of the BamHI B fragment. In the second series of experiments, we constructed a chimeric gene which consisted of the thymidine kinase sequences described above but was fused to a DNA fragment expected to contain the promoter-regulatory region of alpha gene 27 and stretching from approximately -270 to the +55 nucleotide. The chimeric gene in converted cells was amplified upon superinfection with TK(-) virus only when the promoter-regulatory region was in the correct transcriptional orientation relative to the leader and structural sequences of the thymidine kinase gene. The requirements for amplification of the expression of this chimeric thymidine kinase gene were exactly the same as those previously reported for the alpha gene no. 4-thymidine kinase chimera and different from those of the standard (beta) thymidine kinase. We conclude that the positive regulation of expression of alpha gene no. 4 deduced in previous studies may be a general property of alpha genes and that the promoter-regulatory region of alpha gene no. 27 is within a sequence contained between -270 and +55 nucleotides relative to the transcription initiation site.