Nuclear assembly of UGA decoding complexes on selenoprotein mRNAs: a mechanism for eluding nonsense-mediated decay?
Recoding of UGA from a stop codon to selenocysteine poses a dilemma for the protein translation machinery. In eukaryotes, two factors that are crucial to this recoding process are the mRNA binding protein of the Sec insertion sequence, SBP2, and the specialized elongation factor, EFsec. We sought to determine the subcellular localization of these selenoprotein synthesis factors in mammalian cells and thus gain insight into how selenoprotein mRNAs might circumvent nonsense-mediated decay. Intriguingly, both EFsec and SBP2 localization differed depending on the cell line but significant colocalization of the two proteins was observed in cells where SBP2 levels were detectable. We identify functional nuclear localization and export signals in both proteins, demonstrate that SBP2 undergoes nucleocytoplasmic shuttling, and provide evidence that SBP2 levels and localization may influence EFsec localization. Our results suggest a mechanism for the nuclear assembly of the selenocysteine incorporation machinery that could allow selenoprotein mRNAs to circumvent nonsense-mediated decay, thus providing new insights into the mechanism of selenoprotein translation.
Department of Cell and Molecular Biology, University of Hawaii at Manoa, Honolulu, HI 96822, USA.
Lucia A
LA
de Jesus
Peter R
PR
Hoffmann
Tanya
T
Michaud
Erin P
EP
Forry
Andrea
A
Small-Howard
Robert J
RJ
Stillwell
Nadya
N
Morozova
John W
JW
Harney
Marla J
MJ
Berry
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D005815:Genetic Code; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D049790:Nuclear Export Signals; D019913:Nuclear Localization Signals; D010445:Peptide Elongation Factors / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017279:Selenocysteine / Q000235:genetics / Q000378:metabolism; D051140:Selenoproteins / Q000235:genetics* / Q000378:metabolism*
C509159:EFsec protein, mouse; D049790:Nuclear Export Signals; D019913:Nuclear Localization Signals; D010445:Peptide Elongation Factors; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; C121530:SECISBP2 protein, human; D051140:Selenoproteins; D017279:Selenocysteine