The RNA helicase FRH is an ATP-dependent regulator of CK1a in the circadian clock of Neurospora crassa.
The Neurospora clock protein FRQ forms a complex with casein kinase 1a (CK1a) and FRH, a DEAD box-containing RNA helicase with a clock-independent essential function in RNA metabolism. In the course of a circadian period, FRQ is progressively hyperphosphorylated and eventually degraded. Timed hyperphosphorylation of FRQ is crucial for timekeeping of the clock. Here we show that the ATPase activity of FRH attenuates the kinetics of CK1a-mediated hyperphosphorylation of FRQ. Hyperphosphorylation of FRQ is strictly dependent on site-specific recruitment of a CK1a molecule that is activated upon binding. The FRH ATPase cycle regulates the access of CK1a to phosphorylation sites in FRQ in cis, suggesting that FRH is an ATP-dependent remodelling factor acting on the protein complex. We show that the affinity of CK1a for FRQ decreases with increasing FRQ phosphorylation, suggesting functional inactivation of FRQ in the negative feedback loop of the circadian clock before and independent of its degradation.
Biochemistry Centre, University of Heidelberg, Im Neuenheimer Feld 328, Heidelberg D-69120, Germany.
Linda
L
Lauinger
Biochemistry Centre, University of Heidelberg, Im Neuenheimer Feld 328, Heidelberg D-69120, Germany.
Axel
A
Diernfellner
Max Planck Institute of Biochemistry, Am Klopferspitz 18, Martinsried D-82152, Germany.
Sebastian
S
Falk
Biochemistry Centre, University of Heidelberg, Im Neuenheimer Feld 328, Heidelberg D-69120, Germany.
Michael
M
Brunner
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D048148:Casein Kinase Idelta / Q000378:metabolism*; D057906:Circadian Clocks; D005656:Fungal Proteins / Q000378:metabolism*; D009492:Neurospora crassa; D010766:Phosphorylation; D020365:RNA Helicases / Q000378:metabolism*
C087405:FRQ protein, Neurospora crassa; D005656:Fungal Proteins; D000255:Adenosine Triphosphate; D048148:Casein Kinase Idelta; D000251:Adenosine Triphosphatases; C000601633:FRH protein, Neurospora crassa; D020365:RNA Helicases