Mutations in bacterial promoters may increase or decrease the rate of gene trans

Question

Mutations in bacterial promoters may increase or decrease the rate of gene transcription. Promoter mutations that increase transcription are termed up- promoter mutations, and those that decrease transcription are termed down- promoter mutations.   Review the consensus sequence for the -10 box in prokaryotes. The sequence of the -10 region of the promoter for the lac operon is TATGTT.

Comparing the consensus sequence with the lac promoter -10 sequence, would you expect the following mutations to be up- promoter or down- promoter mutations?

A. TATGTT to TATATT

B. TATGTT to TTTGTT

C. TATGTT to TATGAT

Explanation / Answer

Consensus sequence is a sequence of nucleotides having homology to the parent nucleotide sequence after mutation. So, mutations that make a sequence similar to parent sequence makes up-promoter where as mutations that deviate from parent sequence make down-promoters. -10 region is the place of promoter binding which has to be open. So, it has to be made up with AT pairs becuase of their double bonds and easy to be broken. So, the following can be interpreted from the sequences given..

A) Up-promoter mutation

B) Down-promoter mutation

C) Up-promoter mutation

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