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"Which RNA polymerase transcribes 5S rRNA?" is a one-mark question that catches many NEET aspirants, because three of the four rRNAs come from one enzyme and the fourth comes from another. The way to stop guessing is to learn the division of labour as a short story, not a table. This post explains why eukaryotes have several polymerases, what each makes according to NCERT, and where research adds detail.
Where is this in the syllabus?
The NEET (UG) 2026 syllabus lists "Central dogma; Transcription, genetic code, translation" under molecular basis of inheritance, and the CBSE Biology curriculum for 2026-27 lists transcription in the same Class 12 chapter. The text is section 5.5 of the 2026-27 NCERT Class 12 chapter Molecular Basis of Inheritance. Check the syllabus for your exam year.
How is transcription different in bacteria?
NCERT says there is a "single DNA-dependent RNA polymerase that catalyses transcription of all types of RNA in bacteria." On its own, that enzyme can only elongate; it pairs briefly with an initiation factor (σ) to start and a termination factor (ρ) to stop. Because there is no nucleus, translation can begin before transcription has finished.
Eukaryotes add two complications, in NCERT's words. First, "there are at least three RNA polymerases in the nucleus (in addition to the RNA polymerase found in the organelles)", with "a clear cut division of labour". Second, the primary transcript has introns and must be processed.
Which polymerase makes which RNA?
Following NCERT:
RNA polymerase I: the rRNAs 28S, 18S and 5.8S.
RNA polymerase II: the precursor of mRNA, called heterogeneous nuclear RNA (hnRNA).
RNA polymerase III: tRNA, 5S rRNA and snRNAs (small nuclear RNAs).
A way to remember it: polymerase I makes the big rRNAs, II makes the messages, and III makes the small RNAs. 5S rRNA is small, so it goes with the small RNAs to polymerase III.
What happens to the polymerase II product?
hnRNA is not yet usable. NCERT lists three steps:
Splicing: introns are removed and exons joined in a defined order.
Capping: an unusual nucleotide, methyl guanosine triphosphate, is added at the 5' end.
Tailing: 200 to 300 adenylate residues are added at the 3' end, without a template.
Only then does the mRNA leave the nucleus for translation.
Worked example (sample numbers). A polymerase II primary transcript is 6,000 nucleotides long, and its introns total 4,200 nucleotides. How long is the mature mRNA?
Exons: 6,000 − 4,200 = 1,800 nucleotides.
Add the cap (one modified nucleotide) and a tail of 200 to 300 A's.
The mature mRNA is about 2,000 to 2,100 nucleotides, even though most of the gene was intron.
The question checks two ideas at once: introns are cut out, and the tail is added without being coded in the DNA.
How do we know there are several polymerases?
The separation was first reported in 1969 by Robert Roeder and William Rutter, in a Nature paper titled Multiple Forms of DNA-dependent RNA Polymerase in Eukaryotic Organisms. Work on how polymerase II reads genes later earned Roger Kornberg the 2006 Nobel Prize in Chemistry "for his studies of the molecular basis of eukaryotic transcription".
Is NCERT's list the whole story?
For the exam, write NCERT's answer. Research adds two refinements worth knowing so that a wider reading does not confuse you:
Not all snRNAs come from polymerase III. A 2001 review by Nouria Hernandez in the Journal of Biological Chemistry describes snRNA genes as a family in which "some of them are transcribed by RNA polymerase (pol) II and others by pol III": in humans, the U1 and U2 snRNA genes are the prototypes for polymerase II, and U6 for polymerase III.
Plants have more. "At least three" is deliberate wording. Plants have two further multisubunit enzymes, as the title of a review by Haag and Pikaard (2011) puts it: "Multisubunit RNA polymerases IV and V: purveyors of non-coding RNA for plant gene silencing."
Which mistakes cost the most marks?
Putting 5S rRNA with polymerase I. It is polymerase III.
Saying eukaryotes have exactly three polymerases. NCERT says at least three in the nucleus, plus those in organelles.
Giving bacteria three polymerases. Bacteria have one.
Calling hnRNA mature mRNA. It still needs splicing, capping and tailing.
Thinking the poly-A tail is coded in the gene. It is added without a template.
For how transcription compares with replication, see our post on DNA replication and transcription compared, and for the lac operon and the rest of the chapter, the molecular basis of inheritance.
A practice routine
Day 1: Write the three polymerases and their products from memory, then the 5S trap in one sentence.
Day 2: Make ten flashcards, each naming one RNA (tRNA, 18S rRNA, hnRNA, 5S rRNA and so on), and sort them into I, II and III.
Day 3: Redo the mRNA length example with your own numbers, and explain each step aloud.
Day 4: Compare bacterial and eukaryotic transcription in five lines: number of polymerases, factors, processing, location, coupling.
If you want to see the steps in order rather than read them, the Fermi Concept Library covers every concept in biology, each with its own lesson and its place in the map.
Tonight, without notes, write which polymerase makes each of the four rRNAs.
