of the Promoter site
The RNAPol molecule recognizes the beginning of a transcriptional unit for an mRNA as a short DNA sequence motif called a Promoter.The Promoter shown here is approximately 10 bp 'upstream' [5' to] the start site of transcription on the template strand. The same or similar motif sequence is found upstream of many genes, and acts as a signal for transcription.
Note that this "start site" in the DNA is not the same as the "start codon" in the mRNA.
Figure © 2000 by Griffiths et al. ; text © 2014 by Steven M. Carr