34002:

CCA1 is a transcription factor associated with circadian rhythms.

Authors:	Tobin, Elaine, M.(A)Andronis, Christos(A)Green, Rachel, M.(A)Ong, May, S.(A)Sugano, Shoji(A)
Affiliations:	(A): Department of Molecular, Cell and Developmental Biology, U.C.L.A.
Presenter:	Tobin, Elaine M., etobin@ucla.edu

CCA1 is a Myb-related transcription factor that is involved both in phytochrome regulation of Lhcb gene expression (1) and in circadian rhythms of gene expression and various physiological processes (2). It has been proposed that it may, along with the closely related LHY protein (3), be closely associated with a central oscillator in plants. We have isolated a line of Arabidopsis that has a T-DNA insertion in the CCA1 gene, and produces no CCA1 protein (4). These plants show an alteration of the circadian rhythm of gene expression for at least four circadian regulated genes and also shows reduced phytochrome induction of Lhcb gene expression. The results suggest that there is another protein, possibly LHY, whose function is at least partially redundant with that of CCA1. We have found that CCA1 and LHY can interact in vitro, and that LHY can also bind to the Lhcb promoter. Additional experiments have suggested that the binding activity of CCA1 involves phosphorylation by the protein kinase CK2 (5), and we have now found that overexpression of a CK2 b-subunit in transgenic plants affects the circadian rhythms of gene expression. References (1) Wang et al. (1997) Plant Cell 9: 491-507. (2) Wang and Tobin (1998) Cell 93: 1207-1217. (3) Schaffer et al. (1998) Cell 93: 1219-1229. (4) Green and Tobin (1999) Proc. Natl. Acad. Sci. USA. 96: 4176-4179. (5) Sugano et al. (1998) Proc. Natl. Acad. Sci. USA 95: 11020-11025.