Final answer:
Eukaryotic promoters have three main parts: the core promoter with the TATA box, proximal promoter elements like the CAAT box and GC-rich boxes, and distal regulatory elements such as enhancers. They function to initiate transcription by guiding the assembly of transcription factors and RNA polymerase at the start of a gene.
Step-by-step explanation:
The function of promoters in eukaryotes is to initiate transcription by providing a specific sequence that is recognized by transcription factors and RNA polymerase. There are three main regions of a eukaryotic promoter: the core promoter, proximal promoter elements, and distal regulatory elements/enhancers. The core promoter is the most critical region for the formation of the preinitiation complex and usually contains the TATA box, typically located about 25 to 35 bases upstream from the transcription start site. This TATA box has the consensus sequence TATAAA and is bound by the TATA-binding protein (TBP) and transcription factor IID (TFIID), which then recruits additional transcription factors and RNA polymerase II.
Adjacent to the core promoter, the proximal promoter elements can include the CAAT box around -80 bases and GC-rich or octamer boxes whose presence enhances or is required for transcription. Further upstream or at varying positions, distal regulatory elements such as enhancers can greatly affect transcription regulation. Enhancers may be located far from the promoter but can loop back to interact with it. Overall, the promoter regions are vital for the transcription of eukaryotic genes and their evolution is marked by variability. The ability to bind transcription factors accurately and to assemble the transcription machinery effectively is crucial in the regulation of gene expression.