Protein 4.1R binding to eIF3-p44 suggests an interaction between the cytoskeletal network and the translation apparatus

Erythroid protein 4.1 (4.1R) is an 80-kd cytoskeletal protein that stabiliz es the membrane-skeletal network structure underlying the lipid bilayer, Us ing the carboxyl terminal domain (22/24 kd) of 4.1R as bait in a yeast 5-hy brid screen, we isolated cDNA clones encoding a polypeptide of elF3-p44, wh ich represents a subunit of a eukaryotic translation initiation factor 3 (e lF3) complex. The elF3 complex consists of at least 10 subunits that play a n essential role in the pathway of protein translation initiation, Northern blot analysis revealed that elF3-p44 (approximately 1.35 kb) is constituti vely expressed in many tissues, The essential sequence for this interaction was mapped to the carboxyl-terminus of 4.1R (residues 525-622) and a regio n (residues 54-321) of elF3-p44, The direct association between 4.1R and el F3-p44 was further confirmed by in vitro binding assays and coimmunoprecipi tation studies. To characterize the functions of elF3-p44, we depleted elF3 -p44 from rabbit reticulocyte lysates either by anti-elF3-p44 antibody or b y GST/4.1R-80 fusion protein. Our results show that the elF3-p44 depleted c ell-free translation system was unable to synthesize proteins efficiently, The direct association between 4.1R and elF3-p44 suggests that 4.1R may act as an anchor protein that links the cytoskeleton network to the translatio n apparatus.