**Core Concept**
The sigma (σ) subunit of prokaryotic RNA polymerase plays a crucial role in the initiation of transcription by binding to the promoter region of DNA and positioning the RNA polymerase for the start of transcription. This subunit is essential for recognizing and binding to specific promoter sequences, which allows the RNA polymerase to initiate the process of converting DNA into RNA.

**Why the Correct Answer is Right**
The sigma subunit is responsible for the recognition of promoter sequences, which is a critical step in the initiation of transcription. This recognition is facilitated by the binding of the sigma subunit to specific DNA sequences, known as the -10 and -35 regions. The sigma subunit then recruits the RNA polymerase core enzyme, which contains the catalytic activity necessary for the synthesis of RNA. The sigma subunit remains associated with the RNA polymerase during the early stages of transcription but is eventually released as the RNA polymerase reaches the elongation phase.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not related to the sigma subunit of prokaryotic RNA polymerase.
**Option B:** This option refers to a different function of the sigma subunit, which is not accurate.
**Option C:** This option describes a function of the alpha subunit of RNA polymerase, not the sigma subunit.

**Clinical Pearl / High-Yield Fact**
The sigma subunit is essential for the initiation of transcription in prokaryotes, and its recognition of specific promoter sequences is a critical step in the regulation of gene expression. Understanding the role of the sigma subunit is crucial for understanding the mechanisms of transcriptional regulation in prokaryotes.

**Correct Answer: C**. The sigma subunit is responsible for the recognition of promoter sequences and the recruitment of the RNA polymerase core enzyme.