Actin is known to be phosphorylated at tyrosine, serine, or threonine residues in various cells. In cells of Dictyosteliura discoideum, a rise in the tyrosine phosphorylation of actin is observed in response to ATP depletion. An actin fraction rich in phosphotyrosine was obtained by chromatography on the weak anion exchanger Mono-P. Mass spectrometry and amino acid sequencing of protease cleavage products indicated that a single tyrosine residue was phosphorylated. Localization of this residue to position 53 of the actin sequence attributed the modification to a site that is critical for the capability of actin to polymerize. Induction of the tyrosine phosphorylation by heat shock and Cd 2+ ions indicates that this modification of actin is implicated in the response of Dictyostelium cells to stress.
Two new kinases of Dietyostelium discoideum were identified by screening of a 2~gtll expression library with a non-receptor kinases, DPYK1 (=SplA) and DPYK2, have phosphotyrosine specific antibody. Amino-acid sequences derived been published by Tan and Spudich [10]. The elimination of from eDNA and genomic clones indicate that DPYK3 is a one of them (SplA) by gene disruption indicates that this protein of 150 kDa and DPYK4, a protein of 75 kDa. The Ckinase is required for viable spore production [11]. In this terminal fragments of each protein were produced in Escherichia paper we describe two new tyrosine kinases of D. discoideum, coli and shown to be autoeatalytically phosphorylated at tyrosine DPYK3 and DPYK4, and the positions of their catalytic conresidues. A common feature of these kinases is the presence of sensus domains in a dendrogram of protein kinases. A chartwo different sequence stretches in tandem that are related to acteristic of both kinases is the presence of two of these dokinase catalytic domains. The sequence relationships of DPYK3 mains, a peculiarity that will be discussed in terms of its and 4 to other protein kinases, and the positions of their catalytic putative phylogenetic origin. domain sequences within the phylogenetic tree of protein kinases were analysed. Domains I of both kinases and domain II of DPYK3 constitute, together with the catalytic domains of two 2. Material and methods previously described tyrosine kinases of D. discoideum, a branch of their own, separate from the tyrosine kinase domains in sensu 2.1. Library screening and DNA sequencing strictu. Domain II in DPYK4 is found on a different branch close A ~,gtl 1-cDNA expression library of D. discoideum AX3, purchased to serinelthreonine kinases, from Clontech, was screened with iodinated anti-phosphotyrosine mAb 5E2 [12]. The cDNA inserts of phages from 11 plaques recogKey words." Dictyostelium; Dendrogram; Protein tyrosine nized by mAb 5E2 were amplified by PCR with ~.gt 11 specific primers, subcloned into pUC19 and sequenced. Based on cDNA and genomic kinase DNA, the DPYK3 and DPYK4 sequences were completed using sequence specific PCR, inverted PCR, and enrichment mediated PCR approaches [13,14]. The continuity of the obtained sequence fragments was confirmed by the sequencing of two overlapping PCR products of 1. Introduction genomic DNA of D. discoideum AX2 covering the entire DPYK3 coding region including one intron and by the sequencing of one During development of the eukaryotic microorganism Diccontinuous PCR product of genomic DNA comprising the entire tyostelium discoideum, cell interactions are mediated by a ser-DPYK4 coding region plus two introns.ies of chemical signals [1]. These include cAMP and folic acid 2.2. Expression in E. coli that act as chemoattractants, and as ligands in signal trans-A [3-Gal/DPYK3 fusion protein containing amino acids 918-1338 duction pathways controlling gene activities in development, of DPYK3 encoded by the original ~gtl 1-cDNA clone was expressed in E. coli Y1089. C...
Phosphotyrosine-containing proteins in Dictyostelium discoideum were detected by immunoblot analysis and immunoprecipitation using a monoclonal anti-phosphotyrosine antibody. The iodinated antibody recognized on bots a cluster of 205-220 kDa polypeptides and bands of 107 and 60 kDa. The 107 and 60 kDa polypeptides and, in addition, a 82 kDa one became phosphorylated on tyrosine when the immunoprecipitate was incubated with [Y-~~P]ATP. In preparations from differentiating cells the intensity of the label was increased in the 60 kDa band and decreased in the 107 and 205-220 kDa bands.
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