In eukaryotes –
● There are at least `color{Violet}"three RNA polymerases"` in the nucleus (in addition to the RNA polymerase found in the `color{Violet}"organelles"`).

● There is a clear cut `color{Violet}"division of labour"`.

`star` The `color{brown}"RNA polymerase I"` transcribes `color{Violet}"rRNAs"` (`color{Violet}"28S, 18S, and 5.8S"`)

`star` The `color{brown}"RNA polymerase III"` is responsible for transcription of `color{Violet}"tRNA"`, `color{Violet}"5srRNA"`, and `color{Violet}"snRNAs"` (small nuclear RNAs).

`star` The `color{brown}"RNA polymerase II"` transcribes precursor of `color{Violet}"mRNA"`, the heterogeneous nuclear RNA (`color{Violet}"hnRNA"`).

● The `color{Violet}"primary transcripts"` contain both the `color{Violet}"exons and the introns"` which are non-functional.

● Hence, it is subjected to a process called `color{Violet}"splicing"` where the `color{Violet}"introns are removed"` and exons are joined in a defined order.

● The `color{Violet}"hnRNA"` undergo two additional processing called as `color{Violet}"capping and tailing"`.

● In capping an unusual nucleotide (`color{Violet}"methyl guanosine triphosphate"`) is added to the `color{Violet}"5'-end"` of hnRNA.

● In tailing, adenylate residues (200-300) are added at 3'-end in a template independent manner.

● It is the `color{Violet}"fully processed hnRNA"`, now called `color{Violet}"mRNA"`, that is `color{Violet}"transported out"` of the nucleus for translation.

● The significance of such complexities is now beginning to be understood.

● The `color{Violet}"split-gene arrangements"` represent probably an `color{Violet}"ancient feature"` of the genome.

● The `color{Violet}"presence of introns"` is reminiscent of `color{Violet}"antiquity"`, and the process of splicing represents the dominance of RNA-world.