Translational introns: an additional regulatory element in gene expression

The linear expression of a gene can be interrupted by the well-known RNA introns and the recently discovered protein introns. In both cases, splicing mechanisms physically excise the unexpressed segments. In this article we describe a third category of introns that we call 'translational introns'. These functional introns are not excised through a splicing mechanism; instead, the translational machinery bypasses a segment of the coding sequence of an mRNA. We suggest that 'translational introns' are part of a regulatory mechanism that may sense changes in the rate of translation and thereby control the ratio of alternative gene products.