GENETIC-EVIDENCE FOR THE CREATION OF A REINITIATION SITE BY MUTATION INSIDE THE YEAST URA-2 GENE

The ura 2 gene of yeast codes for two enzymatic activities which are translated from a unique messenger RNA in the order carbamoly-phosphate synthetase (CPSase), aspartate transcarbamylase (ATCase) (Lacroute, 1968; Denis-Duphil and Kaplan, 1976). Nonsense mutations in the CPSase region cause a complete loss in ATCase activity by a total polar effect, characteristic of cukaryotic mRNA translation, and due to the unique site of protein initiation present on each messenger (Shaffer et al., 1969). A triple nonsense mutant in the CPSase has been constructed by recombination and ATCase+ revertants have been selected from it. Among seventeen revertants obtained, three had a deletion covering the three nonsense mutations relieving thus the polar effect (Fink and Styles, 1974) but fourteen others examined had retained all the CPSase DNA including the three nonsense mutations; this can be explained in the present state of knowledge only by the creation by mutation of a reinitiation site either for transcription or for translation in the region of the ura 2 gene distal to the last nonsense mutation. © 1979 Springer-Verlag.