Final answer:
Transcription initiation in bacteria is the process where the transcription machinery binds to a specific DNA sequence called the promoter and starts transcribing RNA. The promoter has conserved elements at defined positions, and the sigma factor of RNA polymerase binds to these sequences to initiate transcription.
Step-by-step explanation:
Transcription initiation in bacteria begins at a promoter, which is a specific DNA sequence where transcription machinery binds and starts the transcription process. The initiation site is the nucleotide pair in the DNA double helix from which the first 5' RNA nucleotide is transcribed. Upstream nucleotides are located before the initiation site, while downstream nucleotides are found after the initiation site. Promoters in bacterial genomes have conserved elements at the -10 and -35 positions, known as promoter consensus sequences. These sequences are recognized and bound by the sigma factor of RNA polymerase, which then initiates transcription.