Abstract
Only three immediate early genes (IE) BICP0, BICP4 and BICP22 of Bovine herpesvirus 1 (BoHV-1) are known. These genes are expressed coordinately and their promoters are well characterized. We provide evidence for expression of three additional IE genes of BoHV-1 i.e. UL21, UL33 and UL34. These genes are expressed in the presence of cycloheximide (CH) at the same time as known IE genes. Surprisingly, the promoters of newly identified IE genes (UL21, UL33, UL34) lack the OCT-1 binding site, a considered site of transactivation of the BoHV-1 IE genes. The other difference in the promoters of the newly identified IE genes is the presence of TATA box at near optimal site. However, all the IE genes have similar spatial placements of C/EBPα, DPE and INR elements.
Highlights
The immediate early genes (IE) genes are important for the replication of Bovine herpesvirus 1 (BoHV-1) as they are required for activation of E and L genes and for subsequent down regulation of IE genes themselves[5]
The transcription of the known IE gene, BICP0 as a control was not inhibited by CH (Fig. 1E) while CH effectively inhibited the expression of early gene thymidine kinase (TK) and late gene glycoprotein B without affecting the expression of IE genes (Fig. 1D)
It is assumed that binding of OCT-1 by b-transinducing factor (bTIF) helps in the recruitment of this protein complex to the OCT-1 motif (IFTATGRAAT sequence motif) to initiate the transcription of IE genes in the BoHV-1 infection process[22]
Summary
The IE genes are important for the replication of BoHV-1 as they are required for activation of E and L genes and for subsequent down regulation of IE genes themselves[5]. In HHV-1 infected cells, viral gene expression is initiated when the IE genes are transactivated by α gene trans-inducing factor α-TIF, known as VP16 or Vwm6510,11 but α-TIF does not directly bind DNA, rather it forms a complex with the octamer binding protein (OCT-1) which recognizes and binds to the DNA motifs with the consensus sequence TAATGARAT (OCT-1 motif)[10,12] located in the promoters of the HHV-1 IE genes. This transcriptional program has been well documented in HHV-1, but other members of Alphaherpesvirinae seems to follow somewhat similar transcriptional pattern[12,13,14,15]. C/EBPs are a family of transcription factors that contains a conserved, basicleucine zipper domain involved in DNA binding[26] and belongs to the family of leucine zipper class DNA binding protein[27]
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