Six strains of E. coli (mutants 1–6) that had one of thefollowing mutations (i–vi) affecting the lac operonwere isolated.i. deletion of lacYii. ocmutationiii. missense mutation in lacZiv. inversion of the lac operon (but not an inversion ofthe lacI gene)v. superrepressor mutationvi. inversion of lacZ, Y, and A but not lacI, P, oa. Which of these mutations would prevent the strainfrom utilizing lactose?b. The entire lac operon (including the lacI gene andits promoter) from each of the six E. coli strainswas cloned into a plasmid vector containing an ampicillin resistance gene. Each recombinant plasmidwas transformed into each of the six strains to create partial diploids. In analysis of these strains, mutant 1 was found to carry a deletion of lacY, so thisstrain corresponds to mutation i in the list above.Which of the other types of mutations would be expected to complement mutant 1 in these partial diploids so as to allow lactose utilization?c. In part (b), each strain was plated on ampicillin media in which lactose was the only carbon source.(Ampicillin was included to ensure maintenance ofthe plasmid.) Growth of the transformants is scoredbelow (a + sign indicates growth, a − sign meansno growth). Synthesis of β-galactosidase and permease are both required for growth on this medium.Results of this merodiploid analysis are shown here.Which mutant bacterial strain (1–6) contained eachof the alterations (i–vi) listed previously?1 2 3 4 5 61 − + − + − +2 + − − + − +3 − − − + − +4 + + + + − +5 − − − − − +6 + + + + + +
Six strains of E. coli (mutants 1–6) that had one of the
following mutations (i–vi) affecting the lac operon
were isolated.
i. deletion of lacY
ii. oc
mutation
iii. missense mutation in lacZ
iv. inversion of the lac operon (but not an inversion of
the lacI gene)
v. superrepressor mutation
vi. inversion of lacZ, Y, and A but not lacI, P, o
a. Which of these mutations would prevent the strain
from utilizing lactose?
b. The entire lac operon (including the lacI gene and
its promoter) from each of the six E. coli strains
was cloned into a plasmid vector containing an ampicillin resistance gene. Each recombinant plasmid
was transformed into each of the six strains to create partial diploids. In analysis of these strains, mutant 1 was found to carry a deletion of lacY, so this
strain corresponds to mutation i in the list above.
Which of the other types of mutations would be expected to complement mutant 1 in these partial diploids so as to allow lactose utilization?
c. In part (b), each strain was plated on ampicillin media in which lactose was the only carbon source.
(Ampicillin was included to ensure maintenance of
the plasmid.) Growth of the transformants is scored
below (a + sign indicates growth, a − sign means
no growth). Synthesis of β-galactosidase and permease are both required for growth on this medium.
Results of this merodiploid analysis are shown here.
Which mutant bacterial strain (1–6) contained each
of the alterations (i–vi) listed previously?
1 2 3 4 5 6
1 − + − + − +
2 + − − + − +
3 − − − + − +
4 + + + + − +
5 − − − − − +
6 + + + + + +
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