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Catalytic domain of the Dual-specificity protein kinases, CDC-like kinases Dual-specificity PKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine (S/T) as well as tyrosine residues on protein substrates. 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 S/T residues. In Drosophila, the CLK homolog DOA (Darkener of apricot) is essential for embryogenesis and its mutation leads to defects in sexual differentiation, eye formation, and neuronal development. In fission yeast, the CLK homolog Lkh1 is a negative regulator of filamentous growth and asexual flocculation, and is also involved in oxidative stress response. Vertebrates contain mutliple CLK proteins and mammals have four (CLK1-4). The CLK subfamily is part of a larger superfamily that includes the catalytic domains of other STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",