Molecular mapping of point mutations in the period gene that stop or speed up biological clocks in Drosophila melanogaster.

The pero1 and the pers mutations in Drosophila melanogaster, which seem to eliminate or speed up, respectively, the clocks underlying biological rhythmicity, were mapped to single nucleotides. Chimeric DNA fragments consisting of well-defined wild-type plus mutant DNA subsegments were constructed, introduced into flies by germ-line transformation, and assayed for biological activity. These experiments localized both pero1 and pers to a 1.7-kilobase DNA fragment that is mostly coding DNA. Sequencing of this subsegment from each mutant showed that pero1 is completely accounted for by a nonsense mutation in the third coding exon of a 4.5-kilobase RNA transcribed from this locus. The pers mutation is also a single nucleotide substitution, in the fourth coding exon, which results in a serine-to-asparagine substitution in the per gene protein product. The functional significance of these changes is discussed with reference to the phenotypes of the two mutations.