SksC, a fertilization-related protein kinase in Chlamydomonas, is expressed throughout the cell cycle and gametogenesis, and a phosphorylated form is present in both flagella and cell bodies.
Fertilization in the biflagellated eukaryote, Chlamydomonas, is initiated by flagellar adhesion between gametes of opposite mating types. An early event in the signal transduction pathway induced by these cell-cell interactions is the rapid inactivation of a flagellar protein kinase that phosphorylates a 48 kDa flagellar protein. Molecular cloning and characterization indicated that the 48 kDa substrate, termed SksC, itself is a novel protein kinase. Here, we have determined that its transcript levels were unchanged during prolonged flagellar adhesion. Moreover, resynthesis of new flagellar proteins following deflagellation was not accompanied by increases in transcript levels of SksC, suggesting that expression of this soluble protein kinase might not be restricted to flagella. Immunoblot analysis indicated that expression of SksC was ubiquitous: this soluble protein was found in both flagella and cell bodies and was expressed throughout the cell cycle and gametogenesis. Immunoprecipitation experiments indicated that SksC was phosphorylated in both flagella and cell bodies. Thus, in addition to its potential role in fertilization, this novel protein kinase may play a role in other signaling events in Chlamydomonas.
Department of Cell Biology and Neuroscience, University of Texas, Southwestern Medical Center, Dallas 75235, USA. kurvari@utsw.swmed.edu
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D000818:Animals; D002696:Chlamydomonas / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D003001:Cloning, Molecular; D005407:Flagella / Q000201:enzymology* / Q000502:physiology; D005718:Gametogenesis; D018507:Gene Expression Regulation, Developmental; D017125:Genes, Protozoan; D010766:Phosphorylation; D010940:Plant Proteins; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000235:genetics* / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016053:RNA, Protozoan / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction
D010940:Plant Proteins; D012333:RNA, Messenger; D016053:RNA, Protozoan; D011494:Protein Kinases; C097683:SksC protein, Chlamydomonas reinhardtii; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases