IN-VIVO COOPERATION BETWEEN INTRONS DURING PREMESSENGER RNA PROCESSING

In higher eukaryotes the large number of introns present in most genes implies that the pre-mRNA processing machinery should be efficient an d accurate. Although this could be achieved at the level of each intro n, an attractive alternative would be that interactions between intron s improve the performance of this machinery. In this study we tested t his hypothesis by comparing the processing of transcripts of the tumor necrosis factor beta gene, which differ only by their number of intro ns. We took advantage of the ordered splicing of the three introns pre sent in this gene to design constructs that should generate, as primar y transcripts, molecules that are normally produced by splicing. We es tablished that the apparent splicing rate of intron 3 is increased 2.5 - and 3.5-fold by the presence of one or two other introns on the prim ary transcript, respectively. Similarly, the apparent splicing rate of intron 2 is increased by the presence of intron 1. As these effects i nvolve the splice sites of the upstream intron, these observations sup port the existence of cooperative interactions between introns during pre-mRNA processing.