3 types of bacteriophages ssDNA; complex dsDNA; ssRNA. M13 is this type of phage ssDNA; filamentous, budding. Phi-X-174 is this type of phage circular ssDNA; icosahedral, lytic. T4 is this type of phage complex dsDNA; lytic Lambda is this type of phage complex dsDNA; temperate "temperate" phage means this can be lytic or lysogenic QBeta is this type of phage ssRNA; icosahedral, +strand. R17 is this type of phage ssRNA; icosahedral, +strand. The ssDNA phages we have studied M13, Phi-X-174 The dsDNA phages we have studied T4 (T-even), Lambda Types of attachment used by phages Reversible attachment (adsorption; for T4, tail fibers); Irreversible attachment, where structural changes make receptor binding irreversible (for T4, remainder of tail) The official beginning of infection penetration Types of viral gene expression Gene expression is often staged, as in early gene expression, intermediate gene expression, late gene expression. What often happens during early gene expression conversion of the cell (T4 has nucleases that destroy host chromosome). What usually happens during intermediate gene expression DNA replication What usually happens during late gene expression Assembly proteins are produced (which may require the new genomes from intermediate stage). Discrete stages of infection Attachment; Penetration; Gene Expression; Assembly; Escape. Budding Escape without cell lysis True or False: M13 and Phi-X-174 have similar genomes True This phage has an icosahedral morphology with "spikes" on the vertices Phi-X-174 The B gene of Phi-X-174 is an example of this Frame shifting. It is embedded within gene A. What is remarkable about Phi-X-174's 5.4 kb genome? It is an example of Genetic Economy. It should have room for only 5 genes, but it manages to squeeze in 11. When dealing with a promoter shared by multiple genes, where should a gene be to maximize expression? Adjacent to the terminator sequence, then every transcript will contain the transcribed gene. Features of Genetic Economy Maximize coding capacity of genomes, with overlapping genes (multiple reading frames, same frame/multiple start sites); Multiple functions per protein. A base composition ratio of 1A:1.33T:0.98G:0.75C indicates that... The genome is single stranded, otherwise A=T and G=C. General steps in ssDNA replication ssCircle (infecting genome, +strand) --> dsCircle (the Replicative Form) --> Theta replication --> ssCircle (progeny genome, +strand). Theta replication features Single origin (oriC), bidirectional replication of RF RFs are used for... Replicative Forms are used for rolling circle replication (sigma replication; generates ss progeny DNA). How does phage prevent premature lysis? Regulation of gene expression. Lysis proteins are produced in late gene expression. M13 has multiple promoters. The amount of mRNA produced depends on: the strength of the promoter; distance from terminator M13 infects only through this The f pilus of the host bacterium, which is attacked by the pilot protein. M13 has a somewhat large intergenic region between the start of the genes and the last gene of the circular chromosome. This would be a good spot to ... Put a polylinker. Morphology of M13's capsid Helical; long filament.