Pazour G J, Sineshchekov O A, Witman G B
Worcester Foundation for Biomedical Research, Shrewsbury, Massachusetts 01545, USA.
J Cell Biol. 1995 Oct;131(2):427-40. doi: 10.1083/jcb.131.2.427.
Chlamydomonas has two photobehavioral responses, phototaxis and photoshock. Rhodopsin is the photoreceptor for these responses and the signal transduction process involves transmembrane Ca2+ fluxes. This causes transient changes in flagellar beating, ultimately resulting in phototaxis or photoshock. To identify components that make up this signal transduction pathway, we generated nonphototactic strains by insertional mutagenesis. Seven new phototaxis genes were identified (ptx2-ptx8); alleles of six of these are tagged by the transforming DNA and therefore should be easily cloned. To order the mutants in the pathway, we characterized them electrophysiologically, behaviorally, and structurally, ptx5, ptx6, and ptx7 have normal light-induced photoreceptor currents (PRC) and flagellar currents (FC) but their pattern of swimming does not change in the normal manner when the intraflagellar Ca2+ concentration is decreased, suggesting that they have defects in the ability of their axonemes to respond to changes in Ca2+ concentration. ptx2 and ptx8 lack the FC but have normal PRCs, suggesting that they are defective in the flagellar Ca2+ channel or some factor that regulates it. ptx4 mutants have multiple eye-spots. ptx3 mutants are defective in a component essential for phototaxis but bypassed during photoshock; this component appears to be located downstream of the PRC but upstream of the axoneme.
衣藻有两种光行为反应，趋光性和光休克。视紫红质是这些反应的光感受器，信号转导过程涉及跨膜钙离子通量。这会导致鞭毛摆动的瞬时变化，最终导致趋光性或光休克。为了鉴定构成该信号转导途径的成分，我们通过插入诱变产生了非趋光性菌株。鉴定出了七个新的趋光性基因（ptx2 - ptx8）；其中六个基因的等位基因被转化DNA标记，因此应该很容易克隆。为了在该途径中对突变体进行排序，我们从电生理学、行为学和结构上对它们进行了表征，ptx5、ptx6和ptx7具有正常的光诱导光感受器电流（PRC）和鞭毛电流（FC），但当鞭毛内钙离子浓度降低时它们的游动模式不会以正常方式改变，这表明它们的轴丝对钙离子浓度变化的反应能力存在缺陷。ptx2和ptx8缺乏FC但具有正常的PRC，这表明它们在鞭毛钙离子通道或调节该通道的某些因子方面存在缺陷。ptx4突变体有多个眼点。ptx3突变体在趋光性必需的一个成分上存在缺陷，但在光休克期间被绕过；这个成分似乎位于PRC的下游但轴丝的上游。
