Final answer:
The region immediately adjacent to the starting site for RNA polymerization is called the promoter, which is essential for the initiation of transcription.
Step-by-step explanation:
The region immediately adjacent to the starting site for RNA polymerization is called the promoter. The initiation of transcription begins at this promoter, which is a specific DNA sequence where the transcription machinery, including RNA polymerase, binds to initiate transcription. In bacterial cells, promoters usually have conserved sequences at the -10 and -35 positions upstream of the initiation site. These sequences include the TATA box (TATAAT) at the -10 region and a TTGACA sequence at the -35 region. The promoter is important because it determines the frequency of transcription of the gene.