CMMB 421 Lecture Notes - Lecture 12: Shiga Toxin, Lytic Cycle, Cholera Toxin
28 Dec 2019
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Document Summary
Temperate phages may outnumber virulent ones in nature, and are characterized by the ability to enter a lytic cycle or to lysogenize host cells upon entry. (i. e. become prophages) Prophages confer immunity to subsequent infections by same phage (and sometimes others) Lysogeny usually favoured when cell density and growth rate low, lytic cycle when growth and density high. Lambda best studied temperate phage (and best studied dsdna phage overall). It is a siphovirus, with a 48 kb genome. Linear genome converted to circular inside cell due to annealing of cohesive ss ends, aka cos sites. Circular genome integrated into chromosome if c1 repressor gets upperhand, otherwise phage replicates initially by theta replication then by rolling circle to generate concatemers, which are packaged into nascent phage particles by precise cleavage at cos sites. Prophage can be induced (triggered to exit chromosome and enter lytic cycle) by dna damage which results in sos response and cleavage of c1 repressor by reca protein.
