Roles for Phosphatase PP4 in Rhythmicity and Compensation in the Neurospora Circadian System

Jun 5, 2026bioRxiv : the preprint server for biology

Phosphatase PP4’s role in maintaining and adjusting daily rhythms in Neurospora

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Abstract

Loss of the phosphatase 4 protein results in a significantly shortened circadian period.

Strains lacking phosphatase 4 exhibit a shorter circadian period.
The absence of phosphatase 4 also leads to a notable loss of temperature and nutritional compensation.
PP4 is identified as a heterotrimeric enzyme relevant to the circadian clock.
Two activators of PP4 were discovered, which may regulate circadian period.
PP4 appears to operate in the nucleus and may counteract kinases affecting phosphorylation rates that determine circadian period.
A novel binding partner of PP4, NCU07414, is linked to a dramatically shortened circadian period when lost.

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The circadian clock is a highly conserved timer which allows organisms to anticipate future conditions driven by the 24-hour day on planet Earth. Circadian clocks from fungi to mammals are based on a transcription-translation feedback loop (TTFL) molecular architecture. Progressive phosphorylation of core clock proteins can alter both their activity and stability and is required for all known circadian TTFLs. The mechanism for kinase control of circadian period has been extensively studied; however, the mechanism(s) whereby phosphatases alter period remain less studied. Based on the observation that strains oflacking phosphatase4 display a short circadian period, we investigated regulation of4 and its role in the clockworks. In addition to period shortening, loss of4 results in a significant loss of both temperature and nutritional compensation, consistent with substrates within the core clock. We identify the clock-relevant PP4 phosphatase holoenzyme as a heterotrimer, and identify two activators of PP4 which regulate circadian period. Biochemical and cell biological analyses suggest that PP4 acts in the nucleus, and a mass spectrometry-based screen identified NCU07414, a member of the HSP40 chaperone system, as a novel PP4 binding partner whose loss results in a dramatically shortened period of the clock when ablated. A model consistent with the data suggests that PP4 may act in opposition to kinases to influence the rate of accumulation of the clock-relevant phosphorylations that determine circadian period. Neurospora crassa pp pp pp

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Roles for Phosphatase PP4 in Rhythmicity and Compensation in the Neurospora Circadian System

Abstract

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