What term describes a specific sequence of nucleotides that marks the end of a gene?

The term that describes a specific sequence of nucleotides marking the end of a gene is known as a termination signal. This sequence is crucial in the process of transcription, where it signifies to the RNA polymerase that it should stop synthesizing the RNA molecule. The termination signal ensures that the transcription process does not continue beyond the intended end point of the gene, thus preventing the inclusion of unnecessary information in the RNA transcript.

The other terms listed refer to different aspects of gene expression. A start codon indicates the beginning of translation, where protein synthesis is initiated. The promoter region serves as the binding site for RNA polymerase to start transcription, effectively regulating when a gene is turned on or off. Exon sequences consist of the coding regions of a gene that are retained in the final mRNA product after splicing, and they contribute to the actual protein sequence. Together, these elements play distinct roles in gene expression, but it is the termination signal that specifically denotes where a gene ends.