Identification of CDK- and cyclin-like proteins in the eye of Bulla gouldiana.

Abstract

The ocular circadian rhythm in the eye of Bulla gouldiana is generated by a rhythm in membrane potential of retinal neurons that is driven by alterations in potassium conductance. Since potassium conductance may be modulated by the phosphorylation of potassium channels, the circadian rhythm may reflect rhythmic changes in protein kinase activity. Furthermore, the circadian rhythm recorded from the Bulla eye can be phase shifted by agents that affect protein synthesis and protein phosphorylation on tyrosine residues. Interestingly, the eukaryotic cell division cycle is generated by similar processes. Rhythmic cell division is regulated by periodic synthesis and degradation of a protein, cyclin, and periodic tyrosine phosphorylation of a cyclin-dependent kinase (cdk), p34cdc2. The interaction between these two proteins results in rhythmic kinase activity of p34cdc2. Both cyclin and p34cdc2 are part of two diverse gene families, some of whose members have been localized to post-mitotic cell types with no function yet determined. In the current work, we identify proteins similar to the cdks and cyclin in the eye of Bulla. Neither of these ocular proteins are found in mitotic cells in Bulla, and the cdk-like protein (p40) is specific to the eye. Furthermore, the concentration of the cyclin-like protein (p66) is affected by treatments that phase shift the circadian rhythm. The identification of cdk and cyclin-like proteins in the Bulla eye is consistent with the hypothesis that the biochemical mechanism responsible for generating the ocular circadian rhythm in Bulla is related to the biochemical mechanism that regulates the eukaryotic cell division cycle.