Final answer:
Transcription halts about 140 nucleotides of the initiator in rho-independent termination, making option (a) the correct answer.
Step-by-step explanation:
In the context of molecular biology, transcription termination is a critical process during gene expression. Different types of RNA polymerases in prokaryotic and eukaryotic organisms exhibit distinct mechanisms for termination. For instance, eukaryotic RNA Polymerase II continues transcription beyond the gene's actual end by 1000-2000 nucleotides.
This extra segment is later removed during mRNA processing. Conversely, two main types of termination exist in prokaryotes: the rho-dependent and rho-independent termination. Specifically, rho-independent termination involves the formation of a hairpin structure in the mRNA, which induces stalling of the RNA polymerase when it transcribes a sequence rich in A-T nucleotides, immediately after transcribing a region rich in C-G nucleotides.
For the question asked, transcription halts at rho-independent termination sites due to this structure within about 140 nucleotides of the initiator, which is the correct option to the multiple-choice question given, making (a) the answer.