Final answer:
The main control point for regulating gene expression levels is the promoter region, which binds transcription factors that initiate transcription.
Step-by-step explanation:
The main point of control for regulating gene expression levels is the promoter region. This region is located immediately upstream of the coding sequence of a gene and is responsible for the binding of transcription factors that are essential for initiating transcription. The promoter can vary in length, thereby providing a gene-specific level of control over gene expression. This variability in the promoter region not only affects the accessibility for protein binding but also significantly influences the expression levels of genes as transcription can only commence when transcription factors are bound to the promoter.
Other regions and mechanisms, such as enhancer regions, silencers, and elements of epigenetic regulation, also play roles in gene regulation; however, the promoter region is key in initiating the process of transcription, which is the first essential step in gene expression.