Final answer:
The auxiliary subunits of RNA Polymerase II include Rpb4 and Rpb7, which play regulatory roles or stabilize the complex rather than being essential to the catalytic process of transcription.
Step-by-step explanation:
The question 'Which Rpb subunits are auxiliary?' relates to the structure of RNA Polymerase II (often abbreviated as Pol II or Rpb), which is essential in the process of transcription where DNA is converted into RNA. RNA Polymerase II is a complex enzyme composed of several subunits. Generally, in eukaryotes, it comprises 12 subunits. Key among these include the core subunits, which are essential for the polymerase activity, and the auxiliary or non-essential subunits that play a regulatory role or stabilize the complex. The auxiliary subunits of RNA Polymerase II include Rpb4 and Rpb7, among others. These are not strictly required for the catalytic process of transcription but are associated with various aspects of the enzyme's function, such as transcript elongation under certain conditions, RNA processing, and response to stress.