Abstract
The molecular mechanisms of the pacemakers underlying circadian rhythms are not well understood. One molecule that presumably functions in the circadian clock of Drosophila is the product of the
period (
per) gene, which dramatically affects biological rhythms when mutated. An antibody specific for the per protein labels putative circadian pacemaker neurons and fibers in eyes of two marine gastropods, Aplysia and Bulla. As was found for the Drosophila
per protein, there is a daily rhythm in the levels of the
per-like antigen in Aplysia eyes. Thus, certain molecular features of the
per protein, as well as aspects of the temporal regulation of its expression, may be conserved in circadian pacemakers of widely divergent species.