PROTEIN-SYNTHESIS INITIATION-FACTORS FROM HUMAN HELA-CELLS AND RABBIT RETICULOCYTES ARE SIMILAR - COMPARISON OF PROTEIN-STRUCTURE, ACTIVITIES, AND IMMUNOCHEMICAL PROPERTIES

Five initiation factors, eIF-2, eIF-3, eIF-4A, eIF-4B, and eIF-5, were purified from human [cervical carcinoma] HeLa cells Mehthods of protein fractionation and assays for initiation factors which had been developed for rabbit reticulocytes were suitable for HeLa factors. The initiation factors from HeLa cells are similar to or indistinguishable from the corresponding rabbit reticulocyte factors with respect to specific activities, MW as determined by sodium dodecyl sulfate-polyacrylamide gel electrophorsis, and subunit structure. The MW of eIF-3 particles from both species is about 410,000 as determined by equilibrium sedimentation analytical centrifugation. The partial protease fragmentation patterns of corresponding proteins also are similar and indicate the the primary sequences of the factors are related in the 2 species. Antisera raised in goats against rabbit eIF-3 and human eIF-2, eIF-4A, and eIF-4B cross-react with the cognate factors from both species. On the basis of immunoblotting techniques, eIF-4A is highly conserved, eIF-2.alpha., eIF-3, and eIF-4B are somewhat less conserved, and eIF-2.beta. is the least conserved of the proteins examined. The functional, structural, and immunological results are all consistent with the view that initiation factors from different mammalian cells are very similar.