Jennifer Loros | PubMed Health

PubMed2005

A kinase for light and time.

The eukaryotic filamentous fungus Neurospora crassa has proven to be a dependable model system for the analysis of light-regulated gene expression and circadian rhythmicity. The molecular basis of the core circadian clock is a transcription/translation-based feedback loop in which a heterodimer of the white-collar 1 (WC-1) and white-collar 2 (WC-2) proteins act as a transcription factor to promote expression of the negative elements in the clock, frq mRNA and FRQ protein. Additionally, WC-1 is a flavoprotein that acts as the primary responder to environmental light and, in conjunction with WC-2, is the major photoreceptor for the clock as well as other light-regulated processes. Protein kinase C acts as a light-dependent regulator of the WC-1 protein.

Biological Clocks↗

PubMed2005

Genetic and molecular analysis of phytochromes from the filamentous fungus Neurospora crassa.

Phytochromes (Phys) comprise a superfamily of red-/far-red-light-sensing proteins. Whereas higher-plant Phys that control numerous growth and developmental processes have been well described, the biochemical characteristics and functions of the microbial forms are largely unknown. Here, we describe analyses of the expression, regulation, and activities of two Phys in the filamentous fungus Neurospora crassa. In addition to containing the signature N-terminal domain predicted to covalently associate with a bilin chromophore, PHY-1 and PHY-2 contain C-terminal histidine kinase and response regulator motifs, implying that they function as hybrid two-component sensor kinases activated by light. A bacterially expressed N-terminal fragment of PHY-2 covalently bound either biliverdin or phycocyanobilin in vitro, with the resulting holoprotein displaying red-/far-red-light photochromic absorption spectra and a photocycle in vitro. cDNA analysis of phy-1 and phy-2 revealed two splice isoforms for each gene. The levels of the phy transcripts are not regulated by light, but the abundance of the phy-1 mRNAs is under the control of the circadian clock. Phosphorylated and unphosphorylated forms of PHY-1 were detected; both species were found exclusively in the cytoplasm, with their relative abundances unaffected by light. Strains containing deletions of phy-1 and phy-2, either singly or in tandem, were not compromised in any known photoresponses in Neurospora, leaving their function(s) unclear.

Alternative Splicing↗