Transcription in Eukaryotes
Multiple RNA polymerases in eukaryotes
In eukaryotes there are atleast three different nuclear RNA polymerases, whose properties are given in Table 32.2.

The three RNA polymerases can be distinguished on the basis of their sensitivity to certain inhibitors of transcription, e.g. α amanitin. Each of these enzymes is a large protein (~500,000 daltons), with two large and several (8 < 10) smaller subunits, some of them showing homology to the subunits of E. coll RNA polymerase. The largest subunit (~200,000 daltons) has homology with β', and the second large subunit (- 140,000 daltons) has homology with β subunit of E. coli RNA polymerase (Fig. 32.2). One small subunit of RNA polymerase II also has homology with α subunit. The second largest subunit of RNA polymerase II also shares the catalytic sites of ribonucleases, which may be used for RNA cleavage and may thus help in proof reading (Fig. 32.12).