Final answer:
A down promoter mutation makes the promoter of a gene less like the consensus sequence and inhibits transcription, leading to decreased gene expression.
Step-by-step explanation:
A down promoter mutation causes the promoter of a gene to be less like the consensus sequence and inhibits transcription. Promoter mutations that make the sequence less like the consensus sequence are usually associated with a decreased binding of transcription factors. This change can lead to a lower rate of transcription initiation, meaning that the gene is transcribed less frequently, resulting in lower amounts of mRNA and, consequently, less of the gene product being produced.
By contrasting this with the function of enhancer regions and the binding of transcription factors, one can understand that the interaction of DNA sequences and regulatory proteins plays a critical role in gene expression. Enhancer regions, when bound by transcription factors, typically increase transcription of distant genes, whereas mutations in promoters that remove them from consensus can decrease transcription.