Comparative analysis of avian BMAL1 and CLOCK protein sequences: a search for features associated with owl nocturnal behaviour.

Animals differ widely in the phasing of their daily rhythms with respect to daily environmental rhythms. While birds are predominantly day-active, nocturnal activity is a characteristic feature of the order Strigiformes (owls). To study the evolution of owl night-activity cDNA sequences encoding the circadian core oscillator (CCO) proteins BMAL1 and CLOCK were obtained from barn owl (Tyto alba). The predicted proteins showed high sequence identity with their Galliform homologues (BMAL1: 99%; CLOCK: 95.6%). A computer-predicted chicken BMAL1 casein kinase-1 phosphorylation site is absent from T. alba BMAL1, but also absent from homologues of other six bird species (5 orders) (night-active (n=2), day-active (n=4)) indicating no evolutionary association with night activity. Sequence differences between T. alba and Galliform CLOCK frequently involved serine and threonine residues suggesting potential differences in their phosphorylation. The length of a poly-glutamine string in the CLOCK C-terminus varied between and within 25 species (6 orders) examined, however, no discernible feature distinguishing day and night active species was found. No differences were found between day (n=5) and night (n=7)-active species (12 species, 6 orders) in a region of the PER2 protein implicated in altered rhythm phasing in humans. In conclusion the avian CCO components examined showed strong evolutionary conservation. Molecular evolution associated with owl night-activity may have involved alterations in the CCO relationship with 'output' genes rather than in the molecular structure of the CCO itself.