WC-2 mediates WC-1-FRQ interaction within the PAS protein-linked circadian feedback loop of Neurospora

Publisher Website
Google Scholar
Abstract
Eukaryotic circadian clocks comprise feedback loops where PAS domain‐containing transcriptional activators drive gene expression of negative elements. In Neurospora, clock models posit a White Collar complex (WCC) containing WC‐1 and WC‐2 that activates expression of the central clock gene frequency (frq); FRQ protein is hypothesized to feed back to block the activity of the WCC. We have characterized the WC‐2 protein and its role in this complex: WC‐2 is an abundant constitutive nuclear protein, in contrast to rhythmically expressed FRQ and WC‐1. WC‐2 interacts with WC‐1 and FRQ but, significantly, WC‐1 and FRQ do not interact in the absence of WC‐2. By quantifying the relative numbers of WC‐2, FRQ and WC‐1 proteins and complexes in cell extracts, both the numbers and types of complexes at different circadian times were estimated, yielding results consistent with the model. Constitutive and abundant WC‐2 appears to provide a scaffold allowing for the interaction of two limiting and rhythmically out‐of‐phase proteins, FRQ and WC‐1, and this temporal and physical relationship may be responsible for rhythmic expression of frq.