Final answer:
The RNA polymerases bind to the promoter on DNA, which signals the start of transcription. This site is upstream of the gene and the key to initiating the process of RNA synthesis.
Step-by-step explanation:
The site on DNA to which RNA polymerases bind before initiating transcription is called the promoter. The promoter is located upstream of the gene that is to be transcribed. Its presence signals where the RNA polymerase should attach to the DNA strand to begin the process of transcription. Once RNA polymerase is bound to the promoter, the initiation complex is formed. This marks the beginning of transcription, which involves DNA unwinding to form a transcription bubble where the RNA synthesis will occur.
Other elements that play roles in transcription include the operator, which can regulate the access of RNA polymerase to the genes, the terminator, which signals the end of transcription, the enhancer and silencer regions which can respectively enhance or repress the transcription of the gene. However, it's the promoter that is the critical element for the initiation of transcription by RNA polymerase.