Effect of ochre nonsense mutations on yeast URA1 mRNA stability.

The genetic map of 27 mutants of the URA1 yeast gene has been established by meiotic recombination and 16 nonsense mutations characterized. The half life of URA1 mRNA was determined by two independent methods in the wild-type and in two ochre mutants localized at each extremity of the genetic map. A halflife of 15 min was found for the wild-type and for one of the ochre mutants. This half-life was radically reduced in the other ochre mutant whereas the instantaneous rate of its mRNA synthesis remained constant. After subcloning various endonucleolytic fragments the coding sequence of the URA1 gene was restricted to a 1.65 kb fragment within a 5.7 kb yeast DNA segment. Direct visualization of the URA1 mRNA by Northern hybridization of denatured RNA with a URA1 specific DNA probe revealed a length of 1.5 kb.