SMG-1 is a phosphatidylinositol kinase-related protein kinase required for nonsense-mediated mRNA Decay in Caenorhabditis elegans.
Eukaryotic messenger RNAs containing premature stop codons are selectively and rapidly degraded, a phenomenon termed nonsense-mediated mRNA decay (NMD). Previous studies with both Caenohabditis elegans and mammalian cells indicate that SMG-2/human UPF1, a central regulator of NMD, is phosphorylated in an SMG-1-dependent manner. We report here that smg-1, which is required for NMD in C. elegans, encodes a protein kinase of the phosphatidylinositol kinase superfamily of protein kinases. We identify null alleles of smg-1 and demonstrate that SMG-1 kinase activity is required in vivo for NMD and in vitro for SMG-2 phosphorylation. SMG-1 and SMG-2 coimmunoprecipitate from crude extracts, and this interaction is maintained in smg-3 and smg-4 mutants, both of which are required for SMG-2 phosphorylation in vivo and in vitro. SMG-2 is located diffusely through the cytoplasm, and its location is unaltered in mutants that disrupt the cycle of SMG-2 phosphorylation. We discuss the role of SMG-2 phosphorylation in NMD.
Grimson
Andrew
A
Department of Genetics, University of Wisconsin, 445 Henry Mall, Madison, WI 53706, USA.
O'Connor
Sean
S
Newman
Carrie Loushin
CL
Anderson
Philip
P
D000818:Animals; D017173:Caenorhabditis elegans / Q000033:anatomy & histology / Q000235:genetics / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D006066:Gonads / Q000166:cytology / Q000378:metabolism; D008666:Metalloendopeptidases; D010766:Phosphorylation; D010802:Phylogeny; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*
D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D012333:RNA, Messenger; C121027:SMG-2 protein, C elegans; C472410:SMG-5 protein, C elegans; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; C490966:SMG-1 protein, C elegans; D008666:Metalloendopeptidases; C070738:O-sialoglycoprotein endopeptidase