Promoters that are “close to consensus” (i.e. more similar to
the consensus promoter
sequence) are stronger, resulting in more transcription originating
from these promoters.
Why is transcription initiated more often at these strong
promoters? To answer this question,
explain what a consensus sequence represents and the biochemical
mechanism underlying
promoter strength.
Ans) The consensus sequences in the prokaryotic promoter are -10 (Pribnow box) and -35 sequence.
-10 sequence has TATAAT and -35 sequence has TTGACA. In TATAAT, T80 A95 T45 A60 A50 T96 (the subscript represents the percent occurrence of each of the base. As you can observe that the initiat TA and last T are highly conserved and important for binding RNA polymerase for promoter recognition).
In TTGACA, T82 T84 G78 A65 C54 A45 you can observe that the TT are more conserved. If these initial TT consensus sequence are affected then the strength of promoter will be reduced to a great extent.
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