Synthesis of dihydrofolate reductase and metabolism of related RNA in a methotrexate resistant human cell line infected with herpes simplex virus type 2.

Using a human cell line with amplified gene copy for dihydrofolate reductase (DHFR) and permissive for herpes simplex virus type 2 (HSV-2), the effect of HSV-2 on DHFR synthesis and on the steady-state level of total cellular and nuclear DHFR RNA was examined. There was a reduction in DHFR synthesis accompanied by a proportional decrease in the levels of DHFR messenger RNA (mRNA) 1 hr after infection. Both effects could be induced by HSV pretreated with ultraviolet light and this early virus induced rapid turnover of DHFR mRNA was not dependent on de novo protein synthesis. Analysis of nuclear RNA (nRNA) from uninfected cells by Northern blot hybridization identified a large DHFR nRNA of about 23 kb which probably represents the primary transcript and four processed intermediates of DHFR mRNA ranging in size from 12 to 4.4 kb. The levels of these nRNAs were unchanged during the first hour; however, the 4.4-kb species accumulated in nuclei 2 hr after infection. This effect was induced in the absence of HSV gene expression.