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Catalytic domain of Suppressor of Morphogenetic effect on Genitalia-1 SMG-1 plays a critical role in the mRNA surveillance mechanism known as non-sense mediated mRNA decay (NMD). NMD protects the cells from the accumulation of aberrant mRNAs with premature termination codons (PTCs) generated by genome mutations and by errors during transcription and splicing. SMG-1 phosphorylates Upf1, another central component of NMD, at the C-terminus upon recognition of PTCs. The phosphorylation/dephosphorylation cycle of Upf1 is essential for promoting NMD. In addition to its catalytic domain, SMG-1 contains a FATC (FRAP, ATM and TRRAP, C-terminal) domain at the C-terminus. SMG-1 is a member of the phosphoinositide 3-kinase-related protein kinase (PIKK) subfamily. PIKKs have intrinsic serine/threonine kinase activity and are distinguished from other PKs by their unique catalytic domain, similar to that of lipid PI3K, and their large molecular weight (240-470 kDa). The SMG-1 catalytic domain subfamily is part of a larger superfamily that includes the catalytic domains of other kinases such as the typical serine/threonine/tyrosine protein kinases (PKs), aminoglycoside phosphotransferase, choline kinase, and RIO kinases. |
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