Final answer:
The sigma subunit (σ) of RNA polymerase is the catalytic component involved in the initiation of transcription in prokaryotes, enabling the polymerase to bind specifically to the promoter regions on DNA.
Step-by-step explanation:
The sigma subunit (denoted as σ) of the RNA polymerase is involved in the initiation of transcription in prokaryotes like E. coli. During this stage, the σ subunit is responsible for recognizing the promoter regions on the DNA and facilitating the binding of the core RNA polymerase enzyme to these sites, thereby determining where transcription will start. Without the σ subunit, the core RNA polymerase would bind to random sites on the DNA, leading to non-specific transcription and the production of non-functional mRNA.
Once transcription has been initiated, the σ subunit dissociates from the RNA polymerase, leaving the core enzyme composed of the alpha (α), beta (β), and beta prime (β') subunits to continue transcription during the elongation phase. The complete RNA polymerase with the σ subunit is known as the holoenzyme, while the enzyme without it is referred to as the core enzyme.