Transcription of the human cytomegalovirus glycoprotein gene family in the short unique component of the viral genome.

The HXLF (HindIII X left reading frame) genes are a group of six open reading frames (ORFs) within the short unique component of the human cytomegalovirus genome. Two or more ORFs of the HXLF gene family code for components of the virion envelope glycoprotein complex designated gcII. Transcription of the various HXLF genes in infected cells was analyzed using specific DNA, RNA, and synthetic oligonucleotide probes. Transcription from each of the six HXLF genes was analyzed at immediate early, early, and late times after infection. Even though an enhancer element in six copies is downstream of HXLF6, immediate early cytoplasmic RNAs from the HXLF genes was not detectable. In contrast, early and late cytoplasmic RNAs were detectable for all six HXLF genes. The HXLF1 and 2 genes and the HXLF3 and 4 genes are transcribed as bicistronic mRNAs of 1.6 and 1.7 kb, respectively. The HXLF5 and 6 genes are transcribed as monocistronic mRNAs. In the HXLF4, 5, and 6 transcription units cytoplasmic viral RNAs were detected from both strands. Bidirectional transcription upstream of the enhancer element occurs at only early and late times after infection. The significance of bicistronic mRNA to the formation of the glycoprotein complex gcII requires further investigation.