SPLICING OF A CIRCULAR YEAST PRE-MESSENGER-RNA IN-VITRO

We have tested the fate of a circularized synthetic pre-mRNA transcrip t in a whole cell splicing extract of Saccharomyces cerevisiae. Our re sults demonstrate that this circular precursor RNA is able to induce s pliceosome formation in vitro and that the products of the following s plicing reaction are the lariat-shaped intron, and a mature circular m RNA. Thus, it would appear that free 5' and/or 3' ends are not obligat ory for a splicing reaction to occur, although we find its efficiency to be strongly influenced by the presence or lack of free ends. To our knowledge, this is the first demonstration that a circular pre-mRNA m olecule is recognized as a suitable substrate by an eukaryotic mRNA sp licing apparatus.