Period (gene)

Period (per) is a gene located on the X chromosome of Drosophila melanogaster. Oscillations in levels of both per transcript and its corresponding protein PER have a period of approximately 24 hours and together play a central role in the molecular mechanism of the Drosophila biological clock driving circadian rhythms in eclosion and locomotor activity. Mutations in the per gene can shorten (per^S), lengthen (per^L), and even abolish (per⁰) the period of the circadian rhythm.

Discovery

The period gene and three mutants (per^S, per^L, and per⁰) were isolated in an EMS mutagenesis screen by Ronald Konopka and Seymour Benzer in 1971. The per^S, per^L, and per⁰ mutations were found to complement each other, so it was concluded that the three phenotypes were due to mutations in the same gene. The discovery of mutants that altered the period of circadian rhythms in eclosion and locomotor activity (per^S and per^L) indicated the role of the per gene in the clock itself and not an output pathway. The period gene was first sequenced in 1984 by Michael Rosbash and colleagues. In 1998, it was discovered that per produces two transcripts (differing only by the alternative splicing of a single untranslated intron) which both encode the PER protein.