An Arabidopsis transcript preferentially expressed at the end of the daily
light period codes for the RNA-binding protein AtGRP7. A reverse genetic ap
proach in Arabidopsis thaliana has revealed its role in the generation of c
ircadian rhythmicity: AtGRP7 is part of a negative feedback loop through wh
ich it influences the oscillations of its own transcript. Biochemical and g
enetic experiments indicate a mechanism for this autoregulatury circuit: At
grp7 gene transcription is rhythmically activated by the circadian clock du
ring the day. The AtGPR7 protein accumulates with a certain delay and repre
sses further accumulation of its transcript, presumably at the post-transcr
iptional level. In this respect, the AtGRP7 feedback loop differs from know
n circadian oscillators in the fruitfly Drosophila and mammals based on osc
illating clock proteins that repress transcription of their own genes with
a 24 h rhythm. It is proposed that the AtGRP7 feedback loop may act within
an output pathway from the Arabidopsis clock.