Processing of alpha-globin and ICP0 mRNA in cells infected with herpes simplex virus type 1 ICP27 mutants

Herpes simplex virus (HSV) ICP27 is an essential and multifunctional regula tor of viral gene expression that modulates RNA splicing, polyadenylation, and nuclear export. We have previously reported that ICP27 causes the cytop lasmic accumulation of unspliced alpha-globin pre-mRNA. Here we examined th e effects of a series of ICP27 mutations that alter important functional re gions of the protein on the processing and nuclear transport of alpha-globi n and HSV ICPO RNA. The results demonstrate that ICP27 mutants that are imp aired for growth in noncomplementing cells, including mutants in the N- and C-terminal regions, are defective in the accumulation of alpha-globin pre- mRNA, Unexpectedly, several mutants that are competent to repress the expre ssion of reporter genes in transient transfection assays failed to accumula te unspliced RNA, implying that different mechanisms are responsible for tr ansrepression and pre-mRNA accumulation, Several mutants caused a marked in crease in the length and heterogeneity of the alpha-globin mRNA poly(A) tai l, suggesting that ICP27 may directly or indirectly affect the regulation o f poly(A) polymerase, ICP27 was also required for the accumulation of multi ple ICPO intron-bearing transcripts, but this effect displayed a mutational sensitivity profile different from that of accumulation of unspliced alpha -globin RNA. Moreover, unlike spliced and unspliced alpha-globin RNAs, whic h were efficiently exported to the cytoplasm, spliced and intron-containing ICPO transcripts were predominantly nuclear in localization, and ICP27 was not required for nuclear retention of the spliced message. We propose that these transcript- and ICP27 allele-specific differences may be explained b y the presence of a strong cis-acting ICP27 response element in the alpha-g lobin transcript.