PRD-1, a Component of the Circadian System of Neurospora crassa, Is a Member of the DEAD-box RNA Helicase Family

Apr 1, 2016Journal of biological rhythms

PRD-1, a Circadian Clock Protein in Neurospora crassa, Belongs to the DEAD-box RNA Helicase Family

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Abstract

The prd-1 gene, identified as NCU07839, is associated with disruptions in circadian rhythms in the fungus Neurospora crassa.

The prd-1 mutation lengthens the circadian period in wild-type strains and disrupts FRQ-less rhythms in frq null mutants.
Complementation with the wild-type prd-1 gene corrects rhythm defects both in the complete circadian system and in free-running FRQ-less conditions.
A PRD-1-GFP fusion protein is localized in the nucleus, indicating its potential role in cellular processes.
The prd-1 mutant exhibits abnormal splicing due to a single base pair change in an intron of the gene.
Deletions of other RNA helicases (prd-6 and msp-8) only marginally affect FRQ-less rhythms, suggesting a specific role for PRD-1.

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The circadian rhythms found in almost all organisms are driven by molecular oscillators, including transcription/translation feedback loops (TTFLs). However, TTFL-independent oscillators can drive rhythms in both eukaryotes and prokaryotes. The fungus Neurospora crassa is a model organism for studying the molecular mechanism of the circadian clock. Although a circadian TTFL involving the proteins FRQ, WC-1, and WC-2 is well-characterized in N. crassa, rhythms can still be observed in the absence of this feedback loop. These rhythms are said to be driven by 1 or more FRQ-less oscillator(s) (FLOs). The prd-1 mutation lengthens the period in frq wild type and was previously shown to severely disrupt FRQ-less rhythms in frq null mutants under several different conditions; therefore, the prd-1 gene product is a candidate for a component of a FLO. We report here that prd-1 also disrupts free-running rhythms in wc-1 null mutants, confirming its effects on FRQ-less rhythms. We have now mapped and identified the prd-1 gene as NCU07839, a DEAD-box RNA helicase dbp-2 Complementation with the wild-type gene corrects the rhythm defects of the prd-1 mutant in the complete circadian system (when the FRQ-based TTFL is intact) and also the free-running FRQ-less rhythm on low choline. A PRD-1-GFP fusion protein localizes to the nucleus. The prd-1 mutant has a single base pair change in the first base of an intron that results in abnormally spliced transcripts. FRQ-less rhythms on low choline, or entrained to heat pulses, were only marginally affected in strains carrying deletions of 2 other RNA helicases (prd-6 and msp-8). We conclude that PRD-1 is a member of an RNA helicase family that may be specifically involved in regulating rhythmicity in N. crassa in both the complete circadian system and FLO(s).

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PRD-1, a Component of the Circadian System of Neurospora crassa, Is a Member of the DEAD-box RNA Helicase Family

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