Virology
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	Spring, 2004 Lecture Outline 2/19 UNENVELOPED [NAKED] PLUS-STRAND RNA VIRUSES Basic characteristics of [+] strand RNA viruses 1. plus strand- direct messengers as mRNA; 1.2-1.6 x 106 daltons 2. similar size & shape 3. nucleic acid & protein; no envelopes 4. single protein units in bacteria & plants; up to 4 proteins in Picornaviridae Leviviridae: RNA phage prototypes: MS2, R17, Qb RNA sequence structure; mRNA translation ***2 conservative mech of multiple genes/genome 1. different reading frames c different initiation & termination sites 2. read thru weak termination codon UGA to longer peptide MS2 5' A || coat || pol a3'a aaaaaaaaaaaaaa |lysis| Qb 5' A | A' a a a | pol a3' aaaaaaaa |coat| methods for studying translation RNA phage replication early events 2 forms seen during replication: RF [replicative form] dsRNA- resistant to ribonucleases RI [replicative intermediate] several partial neg strands c plus strand- only partially resistant to nucleases late events in RNA replication lysis protein production: translational interference regulation of production assembly of phage particles RNA phage mutants: Why is the following true? *A protein mutants most frequent mutant found *polymerase mutants least frequent found   Next week: Tuesday: No class- independent work on computer assignment Picornaviridae, Caliciviridae, Nodaviridae, Tobamo- browse CRC, ch 7 & appropriate parts of Wagner, ch 15; on-line .
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