Final answer:
In Rho-independent termination, a string of uracil nucleotides in the RNA molecule plays a key role by forming weak A-U pairs, which, combined with a hairpin loop structure, leads to the release of the newly synthesized mRNA transcript from the DNA template.
Step-by-step explanation:
In Rho-independent termination, the string of U's (uracil nucleotides) in the RNA molecule plays a critical role. This mechanism is distinct from Rho-dependent termination, which involves a protein factor called Rho. During transcription, RNA polymerase synthesizes a new strand of mRNA based on the DNA template. As the polymerase nears the end of the gene being transcribed, it encounters a region with consecutive C-G nucleotides. This causes the mRNA to fold back on itself, forming a stable hairpin loop as the complementary C-G nucleotides within the newly formed mRNA bind together. This loop causes a brief stalling of the polymerase when it starts to transcribe a sequence rich in A-T nucleotides on the DNA template. On the mRNA transcript, this region consists of A-U pairings, where uracil (U) is paired with adenine (A). However, these A-U interactions are relatively weak, and this weakness, when combined with the polymerase stalling at the hairpin structure, leads to a destabilization that prompts the core enzyme to disengage from the DNA, releasing the newly synthesized mRNA transcript.