What are the roles of the different RNA polymerases in eukaryotes?

In eukaryotes, RNA polymerase I synthesises rRNA, RNA polymerase II synthesises mRNA and snRNA, and RNA polymerase III synthesises tRNA and 5S rRNA.

RNA polymerase I, II, and III are the three types of RNA polymerases found in eukaryotic cells. Each of these polymerases has a specific role in RNA synthesis, contributing to the overall process of gene expression.

RNA polymerase I is primarily responsible for the synthesis of ribosomal RNA (rRNA), which forms the core of the ribosome, the cell's protein-making machinery. This polymerase is located in the nucleolus, a specialised subregion within the nucleus, where ribosome assembly occurs. The rRNA molecules synthesised by RNA polymerase I combine with proteins to form the two subunits of the ribosome.

RNA polymerase II is involved in the synthesis of messenger RNA (mRNA) and some small nuclear RNAs (snRNAs). The mRNA molecules are the templates for protein synthesis, carrying the genetic information from DNA to the ribosome. The snRNAs play crucial roles in splicing, a process that removes introns (non-coding regions) from the pre-mRNA to produce the mature mRNA. RNA polymerase II is also involved in the synthesis of some microRNAs, which are involved in the regulation of gene expression.

RNA polymerase III synthesises transfer RNA (tRNA) and the smallest rRNA molecule, 5S rRNA. The tRNA molecules are essential for protein synthesis, carrying the amino acids to the ribosome and matching them to the appropriate codon on the mRNA. The 5S rRNA, together with the other rRNA molecules, forms the structural and functional core of the ribosome.

In summary, the three RNA polymerases in eukaryotes each have distinct roles in the synthesis of different types of RNA, all of which are essential for the process of gene expression and protein synthesis. RNA polymerase I synthesises rRNA, RNA polymerase II synthesises mRNA and some snRNA, and RNA polymerase III synthesises tRNA and 5S rRNA.