Final answer:
The low level of transcription caused by the presence of the core promoter by itself is known as basal transcription. Mutated promoters can alter the binding site for transcription factors, which can either increase or decrease the rate of transcription.
Step-by-step explanation:
The low level of transcription caused by the presence of the core promoter by itself is known as basal transcription. The core promoter contains specific nucleotide sequences, such as the TATA box, that bind to basal transcription factors. These factors help recruit RNA polymerase to the promoter, initiating transcription.
In eukaryotic cells, the core promoter is the minimal region required for basal transcription, while in prokaryotic cells, additional sequences called enhancers and silencers can modulate transcription levels. Mutated promoters can alter the binding site for transcription factors, which can either increase or decrease the rate of transcription.