RNAs Extracted from Herpes Simplex Virus 1 Virions: Apparent Selectivity of Viral but Not Cellular RNAs Packaged in Virions

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Abstract
Following the lead of recent studies on the presence of RNA in virions of human cytomegalovirus, we investigated the presence and identity of RNAs from purified virions of herpes simple virus 1. To facilitate these studies, we designed primers for all known open reading frames (ORFs) and also constructed cDNA arrays containing probes designed to detect all known transcripts. In the first series of experiments, labeled DNA made by reverse transcription of poly(A)+ RNA extracted from infected HEp-2 or rabbit skin cells hybridized to all but two of the probes in the cDNA array. A similar analysis of the RNA extracted from purified extracellular virions derived from infected HEp-2 cells hybridized to probes representing 24 of the ORFs. In the second series of analyses, we reverse transcribed and amplified by PCR RNAs from purified intracellular or extracellular virions derived from infected HEp-2 or Vero cell lines. The positive RNAs were retested by PCR with and without prior reverse transcription to ensure that the samples tested were free of contaminating DNA. The results were as follows. (i) Only a fraction of viral ORF transcripts were represented in virion RNA, and only nine RNAs (UL10, UL34/UL35, UL36, UL42, UL48, UL51, US1/US1.5, US8.5, and US10/US11) were positive in all RT PCR assays. Of these, seven were positive by hybridization to cDNA arrays. (ii) RNA extracted from cells infected with a mutant virus lacking the US8 to US12 genes yielded results similar to those described above, indicating that US11, a known RNA binding protein, does not play a role in packaging RNA in virions. (iii) Cellular RNAs detected in virions were representative of the abundant cellular RNAs. Last, RNA extracted from virions was translated in vitro and the translation products were reacted with antibody to αTIF (VIP16). The immune precipitate contained a labeled protein with the apparent molcular weight of αTIF, indicating that at least one mRNA packaged in virions was intact and capable of being translated. The basis for the apparent selectivity in the packaging of the viral RNAs packaged in virions is unknown.