HOMOLOGOUS AND HETEROLOGOUS EXPRESSION OF A RIBOSOMAL-PROTEIN GENE INPODOSPORA-ANSERINA REQUIRES AN INTRON

Although the role of introns in eucaryotic nuclear genes has been much debated, it remains underinvestigated in fungi. The AS1 gene of Podos pora anserina contains three introns and encodes a ribosomal protein ( S12) belonging to the well-conserved bacterial S19 family. We attempte d to complement the highly pleiotropic mutation AS1-4 with a cDNA enco ding the homologous human (S15 protein (rig gene) under the control of the ASI promoter. In a control experiment the AS1(+) cDNA was unable to complement fully the AS1-4 mutation. It was assumed that the AS1 cD NA was not well expressed and that the ASI gene needed intron(s) to be efficiently expressed. Addition of the first intron of the AS1 gene t o the AS1 and rig cDNAs did indeed allow. complementation of all the p henotypic defects of the AS1-4 mutation. These data lead to two main c onclusions. First, the human S15 ribosomal protein is functional in Po dospora. Second, full expression of the Podospora a AS1 gene requires at least one intron.