Info

(a) 1

Yes

Yes

No

No

(b) 2

Yes

Yes

Some

No

(c) 3

No

No

No

Yes

(d) 4

Yes

Yes

Yes

Yes

Met-Asp-Ala-Tyr-Lys-Gly-Glu-Ala-Pro-Val

A second single-nucleotide mutation occurs in the same gene and suppresses the effects of the first mutation (an intragenic suppressor). With the original mutation and the intragenic suppressor present, the protein has the following amino acid sequence:

Met-Asp-Gly-Ile-Lys-Arg

The ability of various compounds to produce reverse mutations reveals important information about the nature of the original mutation.

(a) Mutations produced by compound 1 are reversed by 5-bromouracil, which produces both A-T:G-C and G-C:A-T transitions. This tells us that compound 1 produces single-base substitutions that may include the generation of either A-T or

G-C pairs. The mutations produced by compound 1 are also reversed by EMS, which, like 5-bromouracil, produces both A-T : G-C and G-C :A-T transitions; so no additional information is provided here. Hydroxylamine does not reverse the mutations produced by compound 1. Because hydroxylamine produces only C-G:T-A transitions, we know that compound 1 does not generate C-G base pairs. Acridine orange, an intercalating agent that produces frameshift mutations, also does not reverse the mutations, revealing that compound 1 produces only single-base-pair substitutions, not insertions or deletions. In summary, compound 1 appears to causes single-base substitutions that generate T-A but not G-C base pairs.

(b) Compound 2 generates mutations that are reversed by 5-bromouracil and EMS, indicating that it may produce G-C or

A-T base pairs. Some of these mutations are reversed by hydroxylamine, which produces only C-G:T-A transitions. This indicates that some of the mutations produced by compound 2 are T-A base pairs. None of the mutations are reversed by acridine orange; so compound 2 does not induce insertions or deletions. In summary, compound 2 produces single-base substitutions that generate both G-C and A-T base pairs.

(c) Compound 3 produces mutations that are reversed only by acridine orange; so compound 3 appears to produce only insertions and deletions.

(d) Compound 4 is reversed by 5 bromouracil, EMS, hydrox-ylamine, and acridine orange, indicating that this compound produces single-base substitutions, which include both G-C and A-T base pairs, and insertions and deletions.

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