Final answer:
A hairpin is an efficient terminator in the rho-independent termination process when it is followed by a stretch of A-U base pairs, after a G/C rich region, causing the RNA polymerase to stall and release the mRNA.
Step-by-step explanation:
A hairpin works as an efficient terminator only when a) It is followed by a stretch of A-U base pairs. In the process of rho-independent termination, the polymerase encounters a region in the DNA template strand that is rich in C-G nucleotides, which causes the mRNA to fold back on itself, creating a stable hairpin structure. This hairpin structure causes the polymerase to stall, and immediately after this G/C rich region, the presence of a region rich in A-T nucleotides – transcribed into A-U base pairs in RNA – leads to weak interactions that cause the core enzyme to release the newly synthesized mRNA transcript.