Spliceosome

The spliceosome is a dynamic molecular machine that removes the introns from protein-coding genes in eukaryotes.  It is composed of 5 small RNA molecules and around 300 proteins.  Here is a video that shows you how the spliceosome works:

More Incurred Cost

I recently tried to show you a pattern that speaks to foresight.  Specifically, one way to infer foresight is if we detect a) a past cost that is b) linked to a future benefit.  Given the growing list of evidence that the last common ancestor of all eukaryotes  had as many or more introns than current metazoans*, we are now in a position to infer a past cost if many/most of the lineages that evolved from this state showed a net loss of introns (costly enough to be removed by selection) and a future benefit if introns play a significant role in multicellular development and/or physiology.

We have seen a hint of future benefit through the manner in which alternative splicing may play a key role in the emergence tissues and organs.  This, and other possibilities, need more exploration.

We have also seen a hint of past cost, where the evolution of chromalveolates was dominated by intron loss.    Well, it turns out that another lineage appears to show the same pattern.