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Mapping of two novel transcripts of bovine papillomavirus type 4
1Beatson Institute for Cancer Research, Bearsden, Glasgow, U.K.
Abstract:
A cDNA library was synthesized using RNA from bovine papillomavirus type 4 (BPV-4)-induced papillomas. The major viral transcript was characterized by sequencing of its cDNA, primer extension mapping and S1 nuclease protection studies. The transcript initiates at multiple sites between nucleotide (nt) 777 and nt 902, contains a splice junction between nt 1016 and nt 3376 and terminates at nt 4034, using the early polyadenylation signal at nt 4009. Sequencing of viral cDNAs and mRNA revealed deviations from the reported genomic sequence between nt 3412 and nt 3460. These resulted in a temporary frameshift, abolished the translation termination codon of the E5a open reading frame (ORF), and introduced a new termination codon in the E4 ORF. The new uninterrupted E5 ORF was found to have greater homology to the E4 ORFs of other papillomaviruses than to their E5 ORFs. The E5 ORF of BPV-4 is joined to a five codon ORF in the leader exon of the major transcript, in the same way as the E4 ORF in the major transcripts of BPV-1 and human papillomavirus type 11. On this basis, it has been redesignated E4, and the viral genomic sequence revised. Two novel transcriptional promoters of BPV-4 were defined: a putative controller of the multiple major RNA start sites around nt 870 and a minor TATA box at nt 691. In addition, minor early region transcripts were mapped which initiate between nt 3071 and nt 3152. None of these transcripts utilizes the splice site at nt 3376. These messages may express E2-encoded functions.
Insights
Researchers characterized the major bovine papillomavirus type 4 (BPV-4) transcript, revealing sequence deviations that led to gene reclassification and identification of novel transcriptional promoters. This study revises the BPV-4 genome sequence and enhances understanding of papillomavirus gene expression.
Area of Science:
- Virology
- Molecular Biology
- Genomics
Background:
- Bovine papillomavirus type 4 (BPV-4) causes papillomas in cattle.
- Understanding BPV-4 gene expression and genomic sequence is crucial for viral research.
Purpose of the Study:
- To characterize the major viral transcript of BPV-4.
- To identify and revise sequence deviations and gene functions within the BPV-4 genome.
- To define novel transcriptional promoters and minor transcripts.
Main Methods:
- cDNA library synthesis from BPV-4 induced papillomas.
- Transcript sequencing, primer extension mapping, and S1 nuclease protection assays.
- Comparison of viral cDNA/mRNA sequences with the reported genomic sequence.
Main Results:
- The major BPV-4 transcript initiates at multiple sites, contains a splice junction, and terminates at nt 4034.
- Sequence deviations between nt 3412-3460 caused a frameshift, altered ORFs (E5a, E4), and led to reclassification of the E5 ORF as E4.
- Two novel transcriptional promoters were identified, along with minor early region transcripts potentially expressing E2 functions.
Conclusions:
- The study provides a revised genomic sequence for BPV-4 based on transcript analysis.
- Gene reclassification (E5a to E4) clarifies papillomavirus gene organization.
- Identification of novel promoters and transcripts advances the understanding of BPV-4 gene regulation.