Final answer:
Abortive cycling in transcription is the process by which RNA polymerase produces short RNA fragments without proceeding to full-length transcription, often occurring multiple times before successful RNA strand synthesis.
Step-by-step explanation:
Abortive cycling refers to an early phase of transcription where RNA polymerase (RNAP) synthesizes short RNA oligonucleotides of around 2-9 nucleotides and restarts transcription repeatedly without leaving the promoter. Essentially, RNA synthesis begins but stalls after a few nucleotides, leading to the dissociation of the short RNA segments and re-initiation by the RNA polymerase. This phenomenon can occur multiple times before a stable RNA-DNA hybrid is formed, and elongation of the RNA transcript proceeds successfully.
Detailed inspections of transcription mention that RNA polymerase also goes through a process known as termination. Termination can happen via a rho-independent mechanism, which is triggered by specific sequences in the DNA template that cause the formation of a hairpin structure in the mRNA, resulting in the dissociation of the RNA polymerase and release of the mRNA transcript. This termination is characterized by sequences rich in C-G nucleotides that form a stable hairpin, followed by a region rich in A-T nucleotides that forms a weak bond with the mRNA, leading to the release of the RNA transcript.