Studies of phytochromes and signal transductbn pathways in cyanobacterial phototaxis

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A gene for a novel flavin-binding protein that is involved in positive phototaxis was cloned from T. elongatus and expressed in E. coli, and expressed. The protein was crystallized and resolved at 2.0 A.Novel phytochrome-like gene pixA was identified as a putative photoreceptor for positive phototaxis. Regulator proteins encoded by nixB and nixC are hypothesized by combinatorial mutagenesis.Regulator genes essential for assembly of motility pili were identified as follows : pilG, pilH, pill, pilJ, pilL-N and pilL-C. The latter two genes were separately expressed on distinct loci on the chromosome.Positive phototaxis photoreceptor PixJ1 protein was isolated from Synechocystis sp. PCC 6803. The protein thus isolated showed novel absorption spectra and difference spectrum in blue and green light regions. The chromophore of PixJ1 was concluded to be a derivative of phycocyanobilin.Four novel flavin-binding photoreceptor proteins were expressed heterologously and their photocycles were partially characterized.The PAS domain proteins of a filamentous cyanobacterium Anabaena sp. PCC 7120 were systematically studied by bioinformatics and biochemical analyses.Genes for the pili subunits were systematically disrupted and identified as pil9,pi110, and pil11.