Varicella-zoster virus gene 63: transcript mapping and regulatory activity

Area of Science:

• Virology
• Molecular Biology
• Gene Regulation

Background:

• The immediate-early (IE) protein encoded by varicella-zoster virus (VZV) ORF63 is homologous to herpes simplex virus type 1 (HSV-1) ICP-22.
• Understanding ORF63's function is crucial for deciphering VZV replication and pathogenesis.

Purpose of the Study:

• To characterize the transcripts and functional role of the VZV ORF63 protein.
• To investigate the regulatory mechanisms influenced by ORF63 during VZV infection.

Main Methods:

• Northern analysis, primer extension, and S1 nuclease assays were employed to map VZV ORF63 transcripts.
• Transient transfection assays were conducted using constructs containing ORF63 and its promoter region to assess its regulatory activity.

Main Results:

• Two VZV transcripts were identified: a 0.9-kb transcript for ORF63 alone and a 1.8-kb transcript read-through into ORF64.
• The ORF63 promoter exhibited weak activation by VZV ORF4 and ORF62, stronger activation by ORF62 alone, and synergistic activation by ORFs 4 and 62.
• ORF63 showed minimal effects on other VZV promoters, no autoregulation, and did not inhibit the ORF62 promoter.

Conclusions:

• VZV ORF63 produces distinct transcripts, with specific transcription start sites and TATA elements.
• ORF63's regulatory role in VZV gene expression appears limited, with its promoter activity modulated by other VZV proteins.
• The findings suggest ORF63 plays a minor role in modulating VZV gene expression compared to other IE genes.