Question

A lacZ mutant of E. coli contains a missense mutation in the middle of the lacZ gene. Based on this information, which of the following statements about this mutant is correct?

1. Translation termination will sometimes occur at the missense codon in lacZ.
2. Factor-dependent transcription termination may occur within the lacZ gene downstream of the missense codon.
3. Factor-independent transcription termination may occur within the lacZ gene downstream of the missense codon.
4. More than one but not all of the above.
5. None of the above.

Answer 1

The definition of missense mutation is - Its a point mutation that changes one base pair in DNA and the change in codon may specify a different amino acid. However, a Missence mutation differs from a Nonsense mutation in which the basepair change leads to the formation of a stop codon and so the translation prematurely terminated.

Based on the definition, the missense mutation in the lacZ gene will not terminate the translation and so option A is wrong. Options B and C are also wrong because there is no relation between a missense mutation and a transcription process. In transcription, the codon is not checked for a mutation its just a copy from DNA.

So the correct option is E, None of the above.