Structural insights into the function of the core-circadian factor TIMING OF CAB2 EXPRESSION 1 (TOC1).
BACKGROUND
The plant circadian clock has at its core a feedback loop that includes TIMING OF CAB2 EXPRESSION 1 (TOC1). This protein has an as of yet unknown biochemical activity. It has been noted that the extreme amino-terminus of this protein is distantly related in sequence to response regulators (RR), and thus TOC1 is a member of the so-called pseudo response regulator (PRR) family. As well, the extreme carboxy-terminus has a small sequence stretch related to the other PRRs and CONSTANS (CO)-like proteins, and this peptide stretch has been termed the CCT (for CONSTANS, CONSTANS-LIKE, TOC1) domain.


METHODS
To extend further our understanding of the TOC1 protein, we performed a ROSETTA structural prediction on TOC1 orthologues from four plant species. Phylogenetic interpretations assisted in model construction.


RESULTS
From our models, we suggest that TOC1 is a three-domain protein: TOC1 has an amino-terminal signaling-domain related to response receivers, a carboxy-terminal domain that could participate both in metal binding and in transcriptional regulation, and a linker domain that connects the two.


CONCLUSIONS
The models we present should prove useful in future hypothesis-driven biochemical analyses to test the predictions that TOC1 is a multi-domain signaling component of the plant circadian clock.
Kolmos
Elsebeth
E
Max Planck Institute for Plant Breeding Research, Carl-von-Linné-Weg 10, D-50829 Cologne, Germany. davis@mpiz-koeln.mpg.de.
Schoof
Heiko
H
Plümer
Michael
M
Davis
Seth J
SJ