In eukaryotic cells, which RNA polymerases are present in the nucleus and what do they transcribe? Choose the best overall statement.

Introduction / Context:
Eukaryotic nuclei contain three specialized RNA polymerases, each dedicated to different RNA classes. Recognizing their co-existence in the nucleus underpins understanding of ribosome biogenesis, mRNA synthesis, and tRNA production.

Given Data / Assumptions:

• RNA polymerase I, II, and III reside in the nucleus (with Pol I concentrated in nucleoli).
• Pol I → 45S rRNA precursor (28S, 18S, 5.8S).
• Pol II → mRNA and many sn/snoRNAs.
• Pol III → tRNA, 5S rRNA, and other small RNAs.

Concept / Approach:
Because all three polymerases function in the nuclear compartment, the comprehensive answer is that the nucleus contains I, II, and III. Each has distinct promoter recognition and sensitivity to inhibitors (for example, alpha-amanitin).

Step-by-Step Solution:
Identify location: nucleus includes nucleoplasm and nucleolus.Assign roles: Pol I (rRNA), Pol II (mRNA), Pol III (tRNA/5S rRNA).Select 'All of these' as correct.

Verification / Alternative check:
Cell fractionation and immunolocalization studies show distinct nuclear distributions of each polymerase.

Why Other Options Are Wrong:
Limiting to a single polymerase ignores the established division of labor. Mitochondrial RNA polymerase operates in mitochondria, not the nucleus.

Common Pitfalls:
Confusing nucleolus (Pol I-rich) with entire nucleus, leading to the mistaken exclusion of Pol II and Pol III.

Final Answer:
All of these (RNA polymerase I, II, and III) are present in the nucleus.