Which RNA polymerase subunit is homologous to Rpb2 in RNAP II?

The RNA polymerase subunit that is homologous to Rpb2 in RNA polymerase II is indeed the B subunit. Rpb2 is a core component of RNA polymerase II, playing a critical role in the enzyme's function during transcription. This subunit is involved in forming the catalytic center of the enzyme, facilitating the synthesis of RNA from a DNA template.

In prokaryotic systems, the RNA polymerase exists as a simpler structure compared to the eukaryotic RNA polymerases. The B subunit in prokaryotic RNA polymerase (specifically in bacterial RNA polymerase) corresponds to Rpb2, as both share structural and functional similarities necessary for the polymerization of nucleotides. Understanding this relationship helps highlight the evolutionary conservation of key components of the transcription machinery across different domains of life.

The other options do not correspond to this homology. The A2 subunit is not present in eukaryotic RNA polymerases, while the α subunit refers more to the assembly and regulation aspects of the bacterial RNA polymerase and does not have a direct homological relationship to Rpb2. Similarly, the b subunit indicates other types of subunits in bacterial RNA polymerase that do not align