How Introns work in Genetric Expression - (Dec/08/2010 )

"The Chimeric intron, which has been demonstrated to significantly increase transgene expression, is included in a variety of the mammalian expression vectors" - Almond, By Brian. "Promega ENotes - Applications." Promega Corporation - Precision Design for Life.

It seems like a chimeric intron choice is works well as a genetic factor for increasing genetic expression, but my question is how to introns work in general to enhance expression and what makes the Chimeric Intron special?

Slicing is coupled to mRNA export mechanism. Thus at least one intron is required for rapid and efficient mRNA export out of the nucleus.

Furthermore, introns are not inert sequences either. It is known that the presence of an intron (usually in its native site in the mRNA) can greatly improve transcription efficiency. Why I am not sure. But some introns are known to carry transcription regulator element and others affect the stability and folding of the RNA transcript. So pick your poison/reason, it is probably right for at least RNA species.