Two E. coli genes, A and B, are known from mapping experiments to be very close
ID: 20083 • Letter: T
Question
Two E. coli genes, A and B, are known from mapping experiments to be very close to each other. A deletion mutation is isolated that eliminates the activity of both A and B. Neither the A nor B protein can be found in the mutant, but a novel protein is isolated in which the amino-terminal 30 amino acids are identical to those of the B gene product and the carboxy-terminal 30 amino acids are identical to those of the A gene product.a) With regard to the 5’ – 3’ orientation of the nontranscribed DNA strand, is the order of the genes AB or BA (4 points)?
b) What number of bases is deleted in the coding region? How do you know?
Explanation / Answer
a) amino terminal or N terminal is always the 5' side. So if B is at the N-terminal, then it will go BA b) 6 basepairs are deleted. Since it says that A and B are still there but just tied together, it means the reading frame hasn't change. Therefore, it just deleted the stop codon of B and the start codon of A. That way, it no longer recognizes when to stop B and continues to make A attached to B. The reason you need to also delete start codon of A is because otherwise, ribosomes can just start at A and not synthesize B at all and it says you can't find any amount of A alone so start codon has to be also deleted
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