Exon repetition in mRNA

The production of different transcripts (transcript heterogeneity) is a fea ture of many genes that may result in phenotypic variation. Several mechani sms, that occur at both the DNA and RNA level have been shown to contribute to this transcript heterogeneity in mammals, all of which involve either t he rearrangement of sequences within a genome or the use of alternative sig nals in linear, contiguous DNA or RNA. Here we describe tissue-specific rep etition of selective exons in transcripts of a rat gene (SA) with a normal exon-intron organization. We conclude that nonlinear mRNA processing can ge nerate tissue-specific transcripts.