Consider a cis-regulatory enhancer sequence in the Escherichia coli chromosome that is located thousands of nucleotide pairs upstream of the gene that it regulates. If the regulatory sequence is mutated to become nonfunctional, the introduction of the wild-type enhancer on a plasmid fails to regulate the gene. This implies that …
A) the regulatory sequence encodes a regulatory protein that binds near the promoter of the target gene and controls RNA polymerase binding.
B) the regulation of the target gene involves looping out of the intervening DNA, and the promoter of the cis-regulatory sequence must be on the same chromosome.
C) the regulatory sequence can bind directly to the RNA polymerase.
D) the regulatory sequence cannot bind to a protein.

Question

Quizplus · Accepted Answer

DNA looping can occur during bacterial gene regulation, where the intervening DNA acts as a tether to enormously increase the probability that the proteins bound near the promoter and those bound to the cis-regulatory sequences will collide with each other. This effect requires that both sequences be on the same DNA molecule, or be somehow linked physically.

Consider a Cis-Regulatory Enhancer Sequence in the Escherichia Coli Chromosome