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

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 ill vitro experiments show that WC-1 and WC-2 are transcriptio n factors regulating the expression of light-induced genes, The WC proteins form homo- and heterodimers in vitro; this interaction could represent a f undamental step in the control of their activity, We demonstrate in vivo th at the WC proteins are assembled in a white collar complex (WCC) and that W C-1 undergoes a change in mobility due to light-induced phosphorylation eve nts. The phosphorylation level increases progressively upon light exposure, producing a hyperphosphorylated form that is degraded and apparently repla ced 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 fu nctional WC-2 is dispensable for this light-specific event, These results s uggest that light-induced phosphorylation and degradation of WC-1 could pla y a role in the transient expression of blue-light-regulated genes. Our fin dings suggest a mechanism by which WC-1 and WC-2 mediate light responses in Neurospora.