The host range of bacteriophages is determined by the attachment proteins on the virus recognizing receptors on the bacterial host and by the ability of the entering phage DNA to escape degradation by host restriction-
enzymes. Most receptor sites for phage are on the cell wall of the bacterium, although some are on pili and flagella.
■ What kind of enzymatic activity does the modification system have?
■ You add an unknown phage to a mixture of F+ and F— cells of E. coli and plate out the bacteria. The bacterial colonies that grow are all F—. How can you explain this phenomenon?
■ A mutation in E. coli results in the loss of both restriction and modification enzymes. Would you expect any difference in the frequency of gene transfer by transduction from Salmonella? Explain.
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