Arabidopsis eIF3e (INT-6) associates with both eIF3c and the COP9 signalosome subunit CSN7

The Arabidopsis COP9 signalosome is a multisubunit repressor of photomorpho genesis that is conserved among eukaryotes, This complex may have a general role in development. As a step in dissecting the biochemical mode of actio n of the COP9 signalosome, we determined the sequence of proteins that copu rify with this complex. Here we describe the association between components of the COP9 signalosome (CSN1, CSN7, and CSN8) and two subunits of eukaryo tic translation initiation factor 3 (eIF3), eIF3e (p48, known also as INT-6 ) and eIF3e (p105), To obtain a biochemical marker for Arabidopsis eIF3, we cloned the Arabidopsis ortholog of the eIF3 subunit eIF3b (PRT1), eIF3e co immunoprecipitated with CSN7, and eIF3c coimmunoprecipitated with eIF3e, eI F3b, CSN8, and CSN1, eIF3e directly interacted with CSN7 and eIF3c, However , eIF3e and eIF3b cofractionated by gel filtration chromatography in a comp lex that was larger than the COP9 signalosome, Whereas eIF3, as detected th rough eIF3b, localized solely to the cytoplasm, eIF3e, like CSN7, was also found in the nucleus. This suggests that eIF3e and eIF3c are probably compo nents of multiple complexes and that eIF3e and eIF3c associate with subunit s of the COP9 signalosome, even though they are not components of the COP9 signalosome core complex. This interaction may allow for translational cont rol by the COP9 signalosome.