In order to characterize three per mutations that eliminate (pero1), shorten (pers), or lengthen (perl) the circadian period of Drosophila melanogaster, the authors sequenced DNA from the per locus in all three strains.
Sequencing revealed the presence of unique single nucleotide substitutions in each of the mutant strains when compared to the wildtype sequence. In perl flies, the mutation was found to be caused by a T-to-A transversion resulting in a valine to aspartic acid amino acid change in the protein. The authors also independently identified the point mutations in pers and pero1 flies. The circadian arrhythmicity in pero1 flies was reported to be attributable to a truncated protein with loss of function, while the rhythm alterations in pers and perl flies were proposed to be attributable to hyper- or hypoactive per protein, respectively, or an increase or decrease in per stability.