TRANSLATIONAL INTRONS - AN ADDITIONAL REGULATORY ELEMENT IN GENE-EXPRESSION

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