Host mRNA Degradation Research Articles

Herpes simplex virus virion host shutoff function.

Herpes simplex virus (HSV) virions contain one or more functions which mediate the shutoff of host protein synthesis and the degradation of host mRNA. HSV type 1 (HSV-1) mutants deficient in the virion shutoff of host protein synthesis (vhs mutants) were isolated and were found to be defective in their ability to degrade host mRNA. Furthermore, it was found that viral mRNAs in cells infected with the vhs 1 mutant have a significantly longer functional half-life than viral mRNAs in wild-type virus-infected cells. In the present study we have mapped the vhs1 mutation affecting the virion shutoff of host protein synthesis to a 265-base-pair NruI-XmaIII fragment spanning map coordinates 0.604 to 0.606 of the HSV-1 genome. The mutation(s) affecting the functional half-lives of host mRNA as well as the alpha (immediate-early), beta (early), and gamma (late) viral mRNAs were also mapped within this 265-base-pair fragment. Thus, the shutoff of host protein synthesis is most likely mediated by the same function which decreases the half-life of viral mRNA. The shorter half-life of infected-cell mRNAs may allow a more rapid modulation of viral gene expression in response to changes in the transcription of viral genes. Interestingly, the vhs1 mutation of HSV-1 maps within a region which overlaps the Bg/II-N sequences of HSV-2 DNA shown previously to transform cells in culture. The possible relationship between the transformation and host shutoff functions are discussed.

Expression of a cellular gene cloned in herpes simplex virus: rabbit beta-globin is regulated as an early viral gene in infected fibroblasts.

We constructed nondefective herpes simplex virus type 1 recombinants bearing the intact rabbit beta-globin gene inserted into the viral gene for thymidine kinase to study the expression of a cellular gene when it is present in the viral genome during lytic viral infections. The globin promoter was activated to high levels during productive infection of Vero cells, giving rise to properly spliced and processed cytoplasmic globin transcripts. Expression of globin RNA occurred with early kinetics, was not affected by blocking viral DNA replication, and was strongly inhibited by preventing viral immediate-early protein synthesis with cycloheximide. These results support the hypothesis that temporal control of herpes simplex virus early gene expression is accomplished by mechanisms that are not restricted to viral promoters. In addition, these data show that a cellular transcript can be correctly processed and can accumulate to high levels during viral infection; this indicates that the mechanisms of virally induced shutoff of host RNA accumulation and degradation of host mRNAs do not depend on sequence-specific differentiation between host and viral RNAs. These findings also suggest that herpesviruses have considerable potential as high-capacity gene transfer vectors for a variety of applications.

Herpes simplex virus-infected cells contain a function(s) that destabilizes both host and viral mRNAs.

The herpes simplex virus virion contains a function that mediates the shutoff of host-protein synthesis and the degradation of host mRNA. Viral mutants affected in this function (vhs mutants) have previously been derived. Cells infected with these mutants exhibit a more stable synthesis of host as well as the immediate early (alpha)-viral proteins. We now show that a function associated with purified virions of the wild-type virus reduces the half-life of host and alpha mRNAs, whereas purified vhs-1 mutant virions lack this activity. The functional half-life of many early (beta)- and late (gamma)-viral mRNAs is also prolonged in mutant virus infections. These studies suggest that the wild-type virion brings into cells a function that indiscriminately reduces the half-life of both host and viral transcripts and that the early translational shutoff of the host is a consequence of this function. This function may facilitate rapid transitions in the expression of groups of genes that are transcriptionally turned on at different times after infection.

Requirement of protein synthesis for the degradation of host mRNA in Friend erythroleukemia cells infected wtih herpes simplex virus type 1

We describe experiments which demonstrate that shortly after infection of Friend erythroleukemia cells with herpes simplex virus (HSV), polyribosomes dissociate and cellular mRNA degrades. Analysis of infected cell extracts on sucrose density gradients demonstrates that the majority of the polyribosomes have dissociated to monoribosomes at 2 h postinfection. Physical measurements of infected-cell RNAs support this conclusion and demonstrate that the polyadenylated RNAs decrease in size. The degradation of mRNA is apparently a stochastic process as judged by the failure to detect a shift in the Crt1/2 when polyadenylated RNA extracted from infected cells at different times is hybridized to globin complementary DNA. In experiments designed to determine whether dissociation of polyribosomes is sufficient to cause degradation of globin mRNA, the amount of globin mRNA in uninfected cells did not change when cells were treated with NaF or pactamycin at concentrations sufficient to dissociate all polyribosomes. In cells infected with UV-irradiated virus polyribosomes dissociate but globin mRNA does not degrade, suggesting that it is possible to separate dissociation from degradation.