Answer:
Because the promoter region is initiation sites for transcription to occur.
Explanation:
Transcription is the first process of gene expression in both eukaryotic and prokaryotic cells. Transcription involves the synthesis of a complementary RNA strand from a DNA template. It is carried out by an enzyme called RNA polymerase which binds to the DNA molecule and adds nucleotides based on the sequence it reads on the DNA.
On the DNA molecule, are sequences of nucleotides which the RNA polymerase recognizes and binds to in order for the transcriptional process to start. These sequences are called PROMOTER regions. They are located upstream i.e. after initiation site, of the DNA. Without these promoter region, RNA polymerase cannot bind to the DNA molecule and hence transcription cannot occur.
