The EMBO Journal Vol. 18,pp. 4961-4968, 1999, Copyright © European Molecular Biology Organization

Role of a white collar-1-white collar-2 complex in blue-light signal transduction

C. Talora, L. Franchi², H. Linden, P. Ballario and G. Macino²

¹ Dipartimento di Genetica e Biologia Molecolare, Centro di Studio per gli Acidi Nucleici, Università di Roma `La Sapienza', Piazzale A.Moro 5, 00185 Rome, <sup>2</sup> Dipartimento di Biotecnologie Cellulari Ed Ematologia, Sezione di Genetica Molecolare, Universita' di Roma `La Sapienza', Policlinico Umberto I, Viale Regina Elena 32, 00161 Rome, Italy, ³ Department of Biology, New York University, New York, NY 1003, USA and ⁴ Lehrstuhl fur Physiologie und Biochemie der Pflanzen, Universitat Konstanz, D-78434 Konstanz, Germany
⁵   Corresponding author
   e-mail: Macino{at}bce.med.uniroma1.it

Mutations in either white collar-1 (wc-1) or white collar-2 (wc-2) lead to a loss of most blue-light-induced phenomena in Neurospora crassa. Sequence analysis and in vitro experiments show that WC-1 and WC-2 are transcription factors regulating the expression of light-induced genes. The WC proteins form homo- and heterodimers in vitro; this interaction could represent a fundamental step in the control of their activity. We demonstrate in vivo that the WC proteins are assembled in a white collar complex (WCC) and that WC-1 undergoes a change in mobility due to light-induced phosphorylation events. The phosphorylation level increases progressively upon light exposure, producing a hyperphosphorylated form that is degraded and apparently replaced in the complex by a newly synthesized WC-1. WC-2 is unmodified and also does not change quantitatively in the time frame examined. Light-dependent phosphorylation of WC-1 also occurs in a wc-2 mutant, suggesting that a functional WC-2 is dispensable for this light-specific event. These results suggest that light-induced phosphorylation and degradation of WC-1 could play a role in the transient expression of blue-light-regulated genes. Our findings suggest a mechanism by which WC-1 and WC-2 mediate light responses in Neurospora.