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Catalytic domain of the Serine/Threonine kinase, Mitogen-activated protein kinase signal-integrating kinase 1 STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. MAPK signal-integrating kinases (Mnks) are MAPK-activated protein kinases and is comprised by a group of four proteins, produced by alternative splicing from two genes (Mnk1 and Mnk2). The isoforms of Mnk1 (1a/1b) and Mnk2 (2a/2b) differ at their C-termini, with the a-form having a longer C-terminus containing a MAPK-binding region. All Mnks contain a catalytic kinase domain and a polybasic region at the N-terminus which binds importin and the eukaryotic initiation factor eIF4G. The best characterized Mnk substrate is eIF4G, whose phosphorylation may promote the export of certain mRNAs from the nucleus. Mnk also phosphorylate substrates that bind to AU-rich elements that regulate mRNA stability and translation. Mnks have also been implicated in tyrosine kinase receptor signaling, inflammation, and cell prolieration or survival. The Mnk subfamily is part of a larger superfamily that includes the catalytic domains of other protein STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
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