Herpesvirus transcription: Altered regulation induced by FUdR

Abstract

The effect of inhibition of viral DNA replication on the regulated production of specific classes of viral transcripts was examined in equine herpesvirus type 1 infected L-M cells. 5-Fluoro-2-deoxyuridine (FUdR) was shown to inhibit viral DNA synthesis and to alter the synthesis of the two classes of viral transcripts that differ in abundance (molar concentration) [Cohen, J. C., Randall, C. C., and O'Callaghan, D. J., Virology 68, 561–565 (1975)]. In uninhibited infection, the ratio of the molar concentration of the major RNA class (most abundant) to minor RNA class (less abundant) was regulated by initiation of viral DNA synthesis since a ratio of 82.7 to 1 for “early” infection (before viral DNA synthesis) decreased to 24 to 1 for “late” infection (after initiation of viral DNA synthesis). Studies employing both standard and summation Scatchard analyses of RNA-DNA hybridization saturation data as well as RNA competition hybridization analysis revealed that in the presence of FUdR viral transcripts comprising the minor RNA class were synthesized in large amounts as compared to uninhibited infection and that sequences usually not transcribed until late were synthesized early in the FUdR-inhibited infection. In addition, it was found that the synthesis of a significant portion of transcripts that comprise the major class of uninhibited infection was blocked in the FUdR-inhibited infection. The ratios of molar concentration of major to minor RNA class present in the FUdR-inhibited infection was found to be 13.9 and 9.2 for early and late times of the infection; these low ratios (as compared to uninhibited infection) and the data of summation Scatchard analysis indicate that reiterated synthesis of certain minor class sequences occurs prematurely (early instead of late) in the presence of FUdR. These findings reveal the importance of the initiation of viral DNA synthesis in the regulation and programming of herpesvirus transcription.