SetK class fulfills the expectation for a C to U change in the coding strand. In this case, the mRNA contains the normal C and thus codes for a WT rII protein even though the DNA contains a mutation. The phage can thus grow in E. coli K even though it will ultimately produce an amber mutation (and thus grow in B). E. coli (FYI: Sam Kaplan became a professor of microbiology here at the U of I where he ran a research program for 30 years). It was known that ochre suppressors can translate amber mutations but amber suppressors cannot translate ochre codons. You have 3 types of strains available for the following experiment: (1) a strain with no suppressors, (2) a strain with a known amber suppressor and (3) a strain with a known ochre suppressor. b. (10 points) They also showed that the amber codon could be mutated to an ochre codon with HA. Starting with several different known rII amber mutants, how could you isolate a mutant with an ochre mutation at the same codon? Would you expect to isolate ochre mutants from all the amber mutants ochre mutants? Why? Answer: If one selects for of several different rII amber mutants on a “revertants” strain containing an ochre suppressor, some revertants will be wild type and some will contain ochre mutations where the HA mutated the UAG codon to a UAA codon However, only wild-type revertants will grow on a suppressor free strain while ochre mutants will fail to grow on the suppressor free strain. Not all amber mutants will yield ochre mutants because the amino acid inserted by the ochre suppressing strain may not make an active rII protein.
SetK class fulfills the expectation for a C to U change in the coding strand. In this case, the mRNA contains the normal C and thus codes for a WT rII protein even though the DNA contains a mutation. The phage can thus grow in E. coli K even though it will ultimately produce an amber mutation (and thus grow in E. coli B). (FYI: Sam Kaplan became a professor of microbiology here at the U of I where he ran a research program for 30 years). It was known that ochre suppressors can translate amber mutations but amber suppressors cannot translate ochre codons. You have 3 types of strains available for the following experiment: (1) a strain with no suppressors, (2) a strain with a known amber suppressor and (3) a strain with a known ochre suppressor. b. (10 points) They also showed that the amber codon could be mutated to an ochre codon with HA. Starting with several different known rII amber mutants, how could you isolate a mutant with an ochre mutation at the same codon? Would you expect to isolate ochre mutants from all the amber mutants ochre mutants? Why? Answer: If one selects for “revertants” of several different rII amber mutants on a strain containing an ochre suppressor, some revertants will be wild type and some will contain ochre mutations where the HA mutated the UAG codon to a UAA codon However, only wild-type revertants will grow on a suppressor free strain while ochre mutants will fail to grow on the suppressor free strain. Not all amber mutants will yield ochre mutants because the amino acid inserted by the ochre suppressing strain may not make an active rII protein.
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