Nitric oxide synthase is induced in sporulation of Physarum polycephalum.
The myxomycete Physarum polycephalum expresses a calcium-independent nitric oxide (NO) synthase (NOS) resembling the inducible NOS isoenzyme in mammals. We have now cloned and sequenced this, the first nonanimal NOS to be identified, showing that it shares < 39% amino acid identity with known NOSs but contains conserved binding motifs for all NOS cofactors. It lacks the sequence insert responsible for calcium dependence in the calcium-dependent NOS isoenzymes. NOS expression was strongly up-regulated in Physarum macroplasmodia during the 5-day starvation period needed to induce sporulation competence. Induction of both NOS and sporulation competence were inhibited by glucose, a growth signal and known repressor of sporulation, and by L-N6-(1-iminoethyl)-lysine (NIL), an inhibitor of inducible NOS. Sporulation, which is triggered after the starvation period by light exposure, was also prevented by 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ), an inhibitor of NO-sensitive guanylate cyclase. In addition, also expression of lig1, a sporulation-specific gene, was strongly attenuated by NIL or ODQ. 8-Bromo-cGMP, added 2 h before the light exposure, restored the capacity of NIL-treated macroplasmodia to express lig1 and to sporulate. This indicates that the second messenger used for NO signaling in sporulation of Physarum is cGMP and links this signaling pathway to expression of lig1.
Golderer
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Institute of Medical Chemistry and Biochemistry, University of Innsbruck, A-6020 Innsbruck, Austria.
Werner
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Leitner
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Gröbner
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Werner-Felmayer
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D018797:Cell Cycle Proteins / Q000235:genetics* / Q000378:metabolism; D003001:Cloning, Molecular; D017124:Conserved Sequence; D006152:Cyclic GMP / Q000378:metabolism; D004790:Enzyme Induction; D005947:Glucose / Q000378:metabolism; D008027:Light; D008969:Molecular Sequence Data; D009569:Nitric Oxide / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000096:biosynthesis / Q000235:genetics*; D010802:Phylogeny; D016839:Physarum polycephalum / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D015800:Protozoan Proteins / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D015398:Signal Transduction; D013170:Spores / Q000201:enzymology / Q000502:physiology
D018797:Cell Cycle Proteins; C400214:Lig1 protein, Physarum polycephalum; D015800:Protozoan Proteins; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D006152:Cyclic GMP; D005947:Glucose