Final answer:
Sigma factors are proteins that help RNA polymerase identify the promoter region during transcription, thus enabling the initiation of transcription in bacteria. Unlike activators that enhance transcription or repressors that inhibit it, sigma factors are concerned primarily with the initial binding of RNA polymerase to DNA.
Step-by-step explanation:
Proteins that aid RNA polymerase in finding the promoter during transcription are called sigma factors. Sigma factors are specifically associated with the initiation of transcription in bacteria. They are a type of basal transcription factor that helps position RNA polymerase at the start of a gene. Other types of regulatory proteins include activators and repressors. Activators enhance the interaction between RNA polymerase and a particular promoter, thereby facilitating transcription, while repressors bind to sequences near or overlapping the promoter region, inhibiting the progression of RNA polymerase.