Received June 28, 2006
Accepted August 11, 2006
A Heteromeric RNA-Binding Protein Is Involved in Maintaining Acrophase and Period of the Circadian Clock
Dobromir Iliev , Olga Voytsekh , Eva-Maria Schmidt , Monika Fiedler , Alla Nykytenko , and Maria Mittag *
Institut für Allgemeine Botanik und Pflanzenphysiologie, Friedrich-Schiller-Universität Jena, Am Planetarium 1 and Dornburger Str. 159, 07743 Jena, Germany
* Corresponding author; email: M.Mittag{at}uni-jena.de.
The RNA-binding protein CHLAMY1 from the green alga Chlamydomonas reinhardtii consists of two subunits. One (named C1) contains three Lysine-homology-motifs and the other (named C3) has three RNA-recognition-motifs. CHLAMY1 binds specifically to UG-repeat sequences and its circadian binding activity is controlled at the posttranslational level, presumably by time-dependent formation of protein complexes consisting of C1 and C3 or C1 alone. Here, we have characterized the role of the two subunits within the circadian system by measurements of a circadian rhythm of phototaxis in strains where C1 or C3 are either up- or down-regulated. Further, we have measured the rhythm of nitrite reductase (NII) activity in strains with reduced levels of C1 or C3. In case of changes in the C3 level (both increases and decreases), the acrophase of the phototaxis rhythm and of the NII rhythm (C3 decrease) was shifted by several hours from subjective midday (maximum in wild-type cells) back towards the night. In contrast, both silencing and overexpression of C1 resulted in disturbed circadian rhythms and arrhythmicity. Interestingly, the expression of C1 is interconnected with that of C3. Our data suggest that CHLAMY1 is involved in the control of the phase angle and period of the circadian clock in C. reinhardtii.
