What signals the termination of transcription?

The termination of transcription is signaled by a terminator. A terminator is a specific sequence of nucleotides in the DNA that indicates where transcription should stop. When RNA polymerase, the enzyme responsible for synthesizing RNA from the DNA template, encounters this terminator sequence, it recognizes it as a signal to detach from the DNA, leading to the release of the newly synthesized RNA molecule.

In contrast, enhancers are sequences that enhance the transcription of associated genes but do not play a direct role in terminating transcription. Promoters are crucial for initiating transcription, as they provide a binding site for RNA polymerase. Operators can regulate gene expression in prokaryotes by controlling the access of RNA polymerase to the promoter, but they do not signal the termination of the transcription process itself. Thus, the terminator is specifically responsible for marking the end of transcription, making it the correct answer.