Virology
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	Spring, 2004 Lecture Outline 3/25 SMALL GENOME DNA VIRUSES: Microviridae & Inoviridae   Intro to small genome DNA viruses: group of unrelated families, only genomic size in common DNA viral advantage- host has all the machinery necessary all members of this loose group- 4-9 genes Microviruses ssDNA, icosahedral phage Inoviruses ssDNA, filamentous phage Parvoviruses ssDNA, icosahedral, naked animal Papovaviruses dsDNA, icosahedral, naked animal Hepadnaviruses dsDNA, icosahedral,enveloped animal Caulimoviruses dsDNA, icosahedral plant Microviruses: prototype- fX 174 a.k.a. fX: host is Salmonella 1st proven to have ssDNA, circular important in recombinant DNA work pilot protein- similar to A protein of RNA phage required for infection; affinity for host lipoprotein replication: 1. ss circle -> ds circle a. DNA pol III makes one copy around strand b. DNA pol I acts as exonuclease, cleaving out primer c. ligase & topoisomerase closes circle d. gyrase causes supercoiling leading to next phase 2. ds circle reversibly supercoils 3. both strands replicated: theta intermediates seen a. supercoiling must be relaxed 1st b. leading strand copied toward replication fork c. other strand copied in Okasaki fragments 4. daughters may be copied in "rolling circle" model a. sigma forms c long tails b. "nickase" cleaves each copy as it comes off 5. early in infection: new DNA may repeat process from beginning transcription & translation: studies show that parent viral ss DNA is + strand copy strand of RF is template for mRNA DNA directed RNA pol binds at promoter sites products exceed number of sites & genomic segments therefore polycistronic one-to-one relationship "violated" in fX: as in Qb c read-through one-to-one respected in structural genes: more product required multifunctionality of proteins: one serves more than one role assembly: appears to be triggered by ss DNA quantity & proteins G & F Inoviruses: prototypes: fd & M13 filamentous, similar to Microviruses in some respects differences: shape- very long & thin, c single molec of ss circular DNA capsid- single protein monomers, c pilot protein @ one end no supertricks of information packaging- only one overlap & no frame shifts structure: coat protein small- 50 kd, in helix around DNA DNA not complimentary, or very short base paired stretches filament vs. icosahedral advantages for recombinant DNA use length increases to accommodate inserts   replication: very similar to fX, including nicking enzyme stops when product V sufficient to coat ss copies assembly: occurs @ membrane product VIII processed to final capsid protein during assembly displaces product V as coat; virion passes out of cell sans lysis host does not die or stop dividing; does multiply @ reduced rate shape and propagation strategies make this phage a fantastic tool   After Spring break: Parvoviridae & Papovaviridae- see CRC, ch 5 & appropriate parts of Wagner, including ch 17, & on-line Adenoviridae & Herpesviridae, Baculoviridae & Iridoviridae- appropriate parts of Wagner, including ch 17 & 18; otherwise same prep as above
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 Updated 1/25/04 by thatcher@sonoma.edu