Lecture 13: DNA Viruses Flashcards
Transcription of viral mRNAs in DNA viruses
Viral mRNAs are generally synthesized by cellular RNA polymerase
General transcription of viral genes in defined, reproducible sequences
-Genes for viral enzymes and regulatory proteins and transcribed early in infection
-Genes for structural proteins are transcribed later
RNA Polymerase I
Transcribes pre-rRNA; no known viral templates
RNA polymerase II
-Transcribed pre-mRNA & snRNA
-Used in most viral DNA’s
RNA Polymerase III
-Transcribes pre-tRNAs, 5S rRNA, U6 snRNA
-Polymerase for some viral DNA’s
Location for DdRp
Nucleus
Variations of nuclear localization
- Viral genome appearing like a chromosome
- Viral ssDNA converted to dsDNA in viral particle dsDNA then imported to nucleus
- Viral RNA is reverse transcribed in virion. cDNA imported into nucleus and integrated into genome
In order to start, transcription machinery must:
-Be directed to initiate transcription at the correct location on a DNA template
-Elongate through the entire gene
-Be directed to terminate transcription at the correct location
Requirements for transcriptional machinery to function
-Cis-acting sequences along DNA
-Trans-acting factors (Accessory proteins)
Transcription by RNA polymerase II
-At least 40 proteins required (Pol II & Accessory proteins)
-Accurate transcription initiated at promoter
-Transcriptional control region
Transcriptional control region (TCR)
Promoter + Additional DNA sequence that controls transcription
Control of transcriptional regulation in Polymerase II
-Cis-acting sequences in DNA
-Trans-acting factors specifically binding to cis-acting sequences to either stimulate or prevent transcription
Regulation of HIV-1 transcription by host and virus encoded factors
-By itself RNA Polymerse II does not elongate from transcriptional control region so HIV produces 2 trans-acting factors: Tar and Tat that work synergistically to recruit other host proteins that stimulate and enhance the processivity of the elongating RNA Pol II complex.
