MCB 421 HOMEWORK #8 FALL 2008
1). Phage HK253 integrates into the E. coli chromosome between the proB and phoE
genes. HK253 specialized transducing phage were isolated which carry the phoE gene.
a. Draw a diagram showing how the LFT lysate could be formed following infection of
E. coli with HK253. [Indicate the expected frequencies for any rare events.]
ANSWER: See figure below.
b. Given a HK253 lysogen, how would you obtain a phoE HFT lysate? [Show a diagram
of how the lysate would be formed.]
ANSWER: See figure below.
c. What is the relative frequency of PhoE+ transductants would you expect from the LFT
and HFT lysates?[Briefly explain your answer.]
ANSWER: About 1/106 phage in the LFT carries the phoE+ gene, while about
1/2 phage in the HFT carries the phoE+ gene.
d. If the transduction was done at a high MOI, many of the resulting PhoE+ transductants
would not be stable. Draw a diagram that shows how the PhoE+ phenotype may be lost
from a bacterium without killing the host.
ANSWER: See figure below.
