Two trans-acting rat-brain proteins, MARTA1 and MARTA2, interact specifically with the dendritic targeting element in MAP2 mRNAs.
Different isoforms of the microtubule-associated protein 2 (MAP2) are somatodendritic components of neurons that seem to regulate the stability of the dendritic cytoskeleton. MAP2 localization into dendrites appears to be a complex multicausal mechanism that involves the specific recruitment of MAP2 mRNAs into dendritic compartments. Recently, we have functionally characterized a 640-nucleotide dendritic targeting element (DTE) in the 3' untranslated region (3' UTR) of MAP2 transcripts that mediates extrasomatic mRNA localization in primary neurons (Blichenberg et al. , 1999). In analogy to molecular mechanisms regulating cytoplasmic RNA translocation in other cell systems, we propose that, in vivo, the cis-acting MAP2-DTE interacts with specific protein factors present in neurons. To identify putative trans-acting DTE-binding proteins, we performed in vitro ultraviolet crosslinking assays. Using this experimental system, two 90-kDa and 65-kDa MAP2-RNA trans-acting proteins, MARTA1 and MARTA2, were identified in rat-brain extracts. Both MARTAs bind with high affinity to the MAP2-DTE, but not to other investigated regions of MAP2 transcripts or the somatically restricted alpha-tubulin mRNA. Moreover, MARTA1 and MARTA2 do not bind significantly to other dendritically localized transcripts encoding vasopressin and arg3.1, nor to a dendritic trafficking element from the mRNA encoding the alpha-subunit of the Ca(2+)/calmodulin-dependent protein kinase II. Binding of MARTA1 and MARTA2 to the MAP2-DTE occurs with an affinity in the nanomolar range. Whereas MARTA1 is clearly detectable in crude lysates, cytosolic and ribosomal salt-wash fractions, and in nuclear extracts, MARTA2 is preferentially found in the ribosomal salt-wash preparation. Neither MARTA is restricted to rat brain, and both are present in a number of other rat tissues. Thus, both proteins may be involved in a variety of nuclear and cytoplasmic events that regulate RNA metabolism in different cell types.
Institute for Cell Biochemistry and Clinical Neurobiology, University Hospital Eppendorf, Hamburg, Germany.
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Rehbein
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Kindler
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Horke
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Richter
D020413:3' Untranslated Regions / Q000235:genetics; D016475:3T3 Cells; D000818:Animals; D001921:Brain / Q000378:metabolism*; D003712:Dendrites / Q000378:metabolism*; D008297:Male; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000235:genetics*; D009474:Neurons / Q000378:metabolism*; D009928:Organ Specificity; D012333:RNA, Messenger / Q000235:genetics; D016601:RNA-Binding Proteins / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D015534:Trans-Activators / Q000378:metabolism*; D014158:Transcription, Genetic
D020413:3' Untranslated Regions; D008869:Microtubule-Associated Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D015534:Trans-Activators; C579810:Fubp3 protein, rat