PAS Domain-Mediated WC-1/WC-2 Interaction Is Essential for Maintaining the Steady-State Level of WC-1 and the Function of Both Proteins in Circadian Clock and Light Responses of Neurospora

Abstract

In the frq-wc-based circadian feedback loops of Neurospora, two PAS domain-containing transcription factors, WHITE COLLAR-1 (WC-1) and WC-2, form heterodimeric complexes that activate the transcription of frequency (frq). FRQ serves two roles in these feedback loops: repressing its own transcription by interacting with the WC complex and positively upregulating the levels of WC-1 and WC-2 proteins. We report here that the steady-state level of WC-1 protein is independently regulated by both FRQ and WC-2 through different posttranscriptional mechanisms. The WC-1 level is extremely low in wc-2 knockout strains, and this low level of expression is independent of wc-1 transcription and FRQ protein expression. In addition, our data show that the PAS domain of WC-2 mediates the interactions of this protein with both WC-1 and FRQ in vivo. Such interactions are essential for maintaining the steady-state level of WC-1 and the proper function of WC-1 and WC-2 in circadian clock and light responses.

We thank Michael Collett, Jay Dunlap, and Jennifer Loros for providing the wc-2 knockout strain prior to its publication. We thank Duojia Pan for critical reading of the manuscript.

This study was supported by grants from the National Institutes of Health (GM 62591) to Y. Liu and from the Robert A. Welch Foundation and the Searle Scholars Program/The Chicago Community Trust to K. H. Gardner. Y. Liu (Louise W. Kahn Scholar) and K. H. Gardner (W. W. Caruth, Jr., Scholar) are both endowed scholars in Biomedical Research at the University of Texas Southwestern Medical Center.