Differential mRNA stabilities of herpes simplex virus type 1

The relative stabilities of Herpes Simplex Virus Type 1 (HSV-1) mRNAs were investigated by determining the half-lives of representative transcripts of each of the temporal classes of genes. For the immediate-early transcripts of the infected cell proteins (ICP) 0 and 27, tissue cultures of Vero cells were infected with HSV-1 and RNA synthesis inhibited by the addition of actinomycin-D at 3 hours post-infection. Single cultures were harvested at regular intervals, and RNA isolated by the guanidinium isothiocyanate/ cesium chloride method. The half-life of a given transcript was determined by quantitating the level of that transcript by Northern analysis at each successive timepoint after the inhibition of RNA synthesis. Half-lives were determined to be 4.2 ± 0.5 hours for the ICP 0 mRNA and 7.2 ± 1.8 hours for the ICP 27 mRNA. The half-life of the early mRNA for the thymidine kinase (TK) gene was indicated to be 8.2 ± 3.1 hours when RNA synthesis was inhibited at 5 hours post-infection. The stability of these mRNAs contrasts with that found for the three late transcripts for the glycoproteins C, E, and H which were found to have half-lives of 14 ± 2.0, 29 ± 6.4, and 25 ± 9.0 hours, respectively, when RNA synthesis was inhibited at 12 hours postinfection. Additionally, the late glycoprotein H mRNA exhibited reduced stability with a half-life of only 11 ± 4.2 hours when examined at 5 rather than 12 hours hours post-infection. It appears that there is a significant difference in the stability of mRNAs transcribed early in infection versus those transcribed late in infection. The mechanism responsible for this difference could have a role in the overall scheme of HSV-1 genetic regulation.