Efficiency of mammalian selenocysteine incorporation.
Five components have thus far been identified that are necessary for the incorporation of selenocysteine (Sec) into approximately 25 mammalian proteins. Two of these are cis sequences, a SECIS element in the 3'-untranslated region and a Sec codon (UGA) in the coding region. The three known trans-acting factors are a Sec-specific translation elongation factor (eEFSec), the Sec-tRNA(Sec), and a SECIS-binding protein, SBP2. Here we describe a system in which the efficiency of Sec incorporation was determined quantitatively both in vitro and in transfected cells, and in which the contribution of each of the known factors is examined. The efficiency of Sec incorporation into a luciferase reporter system in vitro is maximally 5-8%, which is 6-10 times higher than that in transfected rat hepatoma cells, McArdle 7777. In contrast, the efficiency of Sec incorporation into selenoprotein P in vitro is approximately 40%, suggesting that as yet unidentified cis-elements may regulate differential selenoprotein expression. In addition, we have found that SBP2 is the only limiting factor in rabbit reticulocyte lysate but not in transfected rat hepatoma cells where SBP2 is found to be mostly if not entirely cytoplasmic despite having a strong putative nuclear localization signal. The significance of these findings with regard to the function of known Sec incorporation factors is discussed.
Mehta
Anupama
A
Department of Molecular Genetics, Microbiology and Immunology, University of Medicine and Dentistry of New Jersey Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA.
Rebsch
Cheryl M
CM
Kinzy
Scott A
SA
Fletcher
Julia E
JE
Copeland
Paul R
PR
D000818:Animals; D045744:Cell Line, Tumor; D010957:Plasmids; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017279:Selenocysteine / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism
D012333:RNA, Messenger; D017279:Selenocysteine