BASICS of Viral REPLICATION

• (+)-STRAND RNA: The RNA genome can directly serve as an mRNA, because it contains its own 5' cap and 3' Poly-A tail.

  • Isolated mRNA strands are infectious.

• (-)-STRAND RNA: They contain no cap and tail.

  • Isolated mRNA strands are not infectious.

  • They utilize a viral RNA-Dependent RNA-Polymerase to make (1) Subgenomic mRNA's (non-structural and structural proteins), and (2) a complementary (+) RNA genome.

  • The positive-strand RNA genome then serves as a template to make more minus-strand RNA's, to be packaged with the structural proteins.

• Polyproteins are often made by viruses, which are then cleaved, as eukaryotic machinery can't recognize a polycistronic mRNA.

• Double-Stranded DNA: Herpes, Papova, Adeno

  • Early Genes are transcribed by host cell RNA-Polymerase, to form early proteins.

  • These early proteins include a viral DNA-Dependent DNA Polymerase, which then forms progeny DNA.

  • After replication, late genes are transcribed and translated, forming structural proteins.

Category: Microbiology Notes