# Test 2, Lecture 10 Strategy for euk viruses Gain entry to cell; convert cellular machinery; regulate gene expr; replicate genome; assemble; escape Two additional complexities for euk viruses to overcome Multicellular, so tissue aspects; many have immune systems Antibody enhancement of infection Some viruses (Ebola) have features such that an antibody binding to them creates an Ab/Ag complex that is even more efficient at entering cells Cellular aspects for euk viral infections to consider Nucleus and cytoplasm are separate, so does virus enter nucleus or cytoplasm?; nucleus does replication, transcription, and processing; cytoplasm does translation and metabolism. Complexities for euk viral gene expression to consider Separation of transcription and translation, since they occur in physically different compartments; also separated temporally, so no coupled transcription and translation; extensive processing of mRNA; monocistronic mRNA (no operons) Kozak sequence In eukaryotes, the consensus sequence for initiation of translation (ACCAUGG). Scanning ribosome may bypass AUG if not Kozak. PAP Poly-A polymerase hnRNP An mRNA just transcribed by RNA Pol II, with 7meG cap and introns = hnRNA. With proteins that immediately complex with it, hnRNP These steps add the Poly-A tail The mRNA is cleaved at Poly-A addition site, and Poly-A Polymerase adds the A's. Spliceosome snRNA + protein (snRNP) PAB Poly-A Binding Protein: Binds the 3' end of the mRNA (with Poly-A tail) in the initiation complex, while the 5' end is bound, forming a circle. Disease depends on... replication efficiency of the virus; must be at peak efficiency to cause disease. "It's the Virus Stupid" refers to... How much virus can be made in short amount of time Most viruses enter cells by this process Receptor-mediated endocytosis. Receptor-mediated endocytosis. The cell uses this to incorporate material from its surroundings. Viruses take advantage of this by getting the cell to invite them in. The virus attaches to the receptor in the Receptor-mediated endocytosis pathway. This attachment is reversible when there are few contacts. More receptors migrate to initial contact area. When additional contacts are made, the viral attachment becomes irreversible. The membrane folds inward, until it pinches off as a complete endosome inside the cell. This causes the virus to uncoat Acidification of the endosome Uncoating Separates the genome from the capsid and transports genome out of the endosome. This must occur before the endosome fuses with a lysosome, or else the entire endosome including the virus is degraded. This coats the inner membrane Clathrin protein General steps of shift to eukaryotic viral synthesis Immediate block of protein synthesis; block RNA synthesis; block DNA synthesis; synthesis of all molecules resumes, but now the molecules are for viral multiplication; viral synthesis is staged.