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Catalytic domain of the Dual-specificity protein kinase, CDC-like kinase 3 Dual-specificity PKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine as well as tyrosine residues on protein substrates. CLK3 is predominantly expressed in mature spermatozoa, and might play a role in the fertilization process. CLKs are involved in the phosphorylation and regulation of serine/arginine-rich (SR) proteins, which play a crucial role in pre-mRNA splicing by directing splice site selection. SR proteins are phosphorylated first by SR protein kinases (SRPKs) at the N-terminus, which leads to its assembly into nuclear speckles where splicing factors are stored. CLKs phosphorylate the C-terminal part of SR proteins, causing the nuclear speckles to dissolve and splicing factors to be recruited at sites of active transcription. Based on a conserved "EHLAMMERILG" signature motif which may be crucial for substrate specificity, CLKs are also referred to as LAMMER kinases. CLKs autophosphorylate at tyrosine residues and phosphorylate their substrates exclusively on serine/threonine residues. The CLK3 subfamily is part of a larger superfamily that includes the catalytic domains of other protein serine/threonine PKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase. |
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