Question

How is a continuous linear sequence of genes on mRNA formed in eukaryotes?

Answer 1

In eukaryotes, many genes are split genes: coding regions called exons are interrupted by non-coding regions called introns. Transcription first produces a primary RNA transcript containing both.

1. Introns are removed from the primary transcript by RNA splicing.
2. The exons are joined in their original order, forming a continuous coding sequence in the mature mRNA.
3. The RNA is also processed by addition of a cap at the [5'] end and a poly-A tail at the [3'] end. The mature mRNA then exits the nucleus for translation.

Splicing therefore brings the expressed coding regions together in a continuous linear sequence in mature eukaryotic mRNA.