Characterization of the human cytomegalovirus UL105 gene and identification of the putative helicase protein.

We have characterized the transcription unit for the human cytomegalovirus UL105 gene and identified its putative protein product. The UL105 gene product is proposed to mediate helicase activity in the assembled helicase-primase complex. The two other putative proteins in this complex are the gene products of UL102 (primase-associated factor) and UL70 (primase). Using Northern blot analysis we have determined that the UL105 transcript is a 3.4-kb message that can be detected as early as 24 hr postinfection in the presence of phosphonoformic acid but not in the presence of cycloheximide. Subsequent primer-extension analysis showed a transcriptional start site upstream of a consensus TATA sequence and just downstream of a CCAAT box sequence motif. In addition, we have identified an infected cell protein with an approximate molecular weight (M(r)) of 110 kDa using anti-peptide antiserum. This same antiserum detected proteins of the same M(r) as those produced from two expression systems where the protein from the 981-amino-acid UL105 open reading frame was overexpressed, suggesting that the ATG located at nt 151,850 of the genomic sequence is utilized in the context of the virus genome.