a new mutation affecting frq-less rhythms in the circadian system of neurospora crassa一个新的突变影响frq-less节奏在粗糙脉孢菌的生理系统.pdfVIP

A New Mutation Affecting FRQ-Less Rhythms in the Circadian System of Neurospora crassa 1¤ 1,2 1 1 1 Sanshu Li , Kamyar Motavaze , Elizabeth Kafes , Sujiththa Suntharalingam , Patricia Lakin-Thomas * 1 Department of Biology, York University, Toronto, Canada, 2 Department of Microbiology, Tehran North Branch, Islamic Azad University, Tehran, Iran Abstract We are using the fungus Neurospora crassa as a model organism to study the circadian system of eukaryotes. Although the FRQ/WCC feedback loop is said to be central to the circadian system in Neurospora, rhythms can still be seen under many conditions in FRQ-less (frq knockout) strains. To try to identify components of the FRQ-less oscillator (FLO), we carried out a mutagenesis screen in a FRQ-less strain and selected colonies with altered conidiation (spore-formation) rhythms. A mutation we named UV90 affects rhythmicity in both FRQ-less and FRQ-sufficient strains. The UV90 mutation affects FRQ- less rhythms in two conditions: the free-running long-period rhythm in choline-depleted chol-1 strains becomes arrhythmic, and the heat-entrained rhythm in the frq 10 knockout is severely altered. In a FRQ-sufficient background, the UV90 mutation causes damping of the free-running conidiation rhythm, reduction of the amplitude of the FRQ protein rhythm, and increased phase-resetting responses to both light and heat pulses, consistent with a decreased amplitude of the circadian oscillator. The UV90 mutation also has small but significant effects on the period of the conidiation rhythm and on growth rate. The wild-type UV90 gene product appears to be required for a functional FLO and for sustained, high-amplitu