CIRCADIAN CYCLING OF A PERIOD-BETA-GALACTOSIDASE FUSION PROTEIN IN DROSOPHILA - EVIDENCE FOR CYCLICAL DEGRADATION

The authors analyzed circadian features of two period-lacZ (peu-lacZ) fusion genes in transgenic strains of Drosophila. Both genes manifest circadian fluctuations of mRNA levels, but fluctuations of only the la rger chimeric protein are apparent. Fusion protein cycling is indistin guishable from the behavior of wild-type per protein (PER), including apparent temporal regulation of phosphorylation state. Several argumen ts indicate that the difference in the two constructs is proper regula tion at the level of protein turnover: the smaller protein has much hi gher levels; a P-galactosidase degradation product is visible in both strains but fails to manifest cycling, presumably due to a long half-l ife; and only the noncycling proteins accumulate as a function of adul t age. The large cycling fusion protein also undergoes modest cycling in an arrhythmic per(01) background. This is Light dependent, resemble s the regulation of the timeless protein (TIM) by light, and reflects a documented fusion protein-TIM interaction. The results are discussed with respect to the posttranscriptional regulation that is necessary for proper cycling of both PER and TIM as well as for clock function.