title: Purification and characterization of two initiation factors required for maximal activity of a highly fractionated globin mRNA translation system.
abstract: Two additional initiation factors (IF-M4 and IF-M5) have been purified and characterized both physically and biologically. IF-M4 is active as a single polypeptide chain with a molecular weight of 48,000. In contrast, IF-M5 is active as a complex with a molecular weight of about 500,000 and consists of seven major and several minor polypeptide components. Analysis of IF-M5 in two polyacrylamide gel electrophoresis systems indicated that one of the major polypeptide chains of IF-M5 was the 35,000 dalton subunit of IF-MP. This analysis also revealed that IF-M2A, IF-M3, and elongation factor 2 were present as minor components. Both IF-M4 and IF-M5 are required to achieve maximal activity in an assay system dependent on exogenous globin mRNA, but neither factor has been observed to stimulate model reactions that utilize artificial templates [poly(U) or AUG].
mesh_terms: D000818:Animals; D002474:Cell-Free System; D005914:Globins; D008970:Molecular Weight; D010445:Peptide Elongation Factors / Q000032:analysis; D010448:Peptide Initiation Factors / Q000032:analysis / Q000302:isolation & purification*; D011072:Poly U / Q000378:metabolism; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism*; D011817:Rabbits; D012156:Reticulocytes; D012261:Ribonucleoproteins / Q000032:analysis
chemical_list: D010445:Peptide Elongation Factors; D010448:Peptide Initiation Factors; D012333:RNA, Messenger; D012261:Ribonucleoproteins; D011072:Poly U; D005914:Globins