Promoters are DNA sequences located in the 5' region adjacent to the transcriptional start site. RNA polymerase and accessory proteins (transcription factors) bind to the promoter to initiate production of an mRNA transcript. Interactions of proteins at the promoter regulate gene actvity by activating or repressing transcription.
The majority of eukaryotic mRNAs contain a tract of A residues at the end. These polyA-tails are not encoded in the DNA. Rather, they are added to the pre-mRNA "post-transcriptionally" (after transcription). The end of pre-mRNA is cut by a specific enzyme