title: Euglena gracilis chloroplast initiation factor 2. Identification and initial characterization.
abstract: The chloroplast protein synthesis factor responsible for the binding of fMet-tRNAMeti to chloroplast 30 S ribosomal subunits (IF-2chl) has been identified in whole cell extracts of Euglena gracilis. The IF-2chl activity is present in considerably higher amounts in extracts of light-grown cells than in extracts of dark-grown cells. About 90% of this activity is found in the postribosomal supernatant of the cell. Chromatography on phosphocellulose results in the partial purification of IF-2chl and separates the chloroplast factor from the cytoplasmic factor eIF-2A. The binding of fMet-tRNAMeti to chloroplast 30 S subunits is message-dependent as observed for prokaryotic systems. In addition, GTP stimulates the IF-2chl-dependent reaction 3-fold. The binding reaction shows broad monovalent and divalent cation optima. The activity of IF-2chl is stimulated 2-fold by the addition of either Escherichia coli IF-1 or IF-3, and 4-fold by the inclusion of both factors. Chloroplast IF-2 is quite active on the homologous 30 S ribosomal subunits but shows little activity on E. coli 30 S or wheat germ 40 S subunits.
mesh_terms: D002736:Chloroplasts / Q000032:analysis*; D002850:Chromatography, Gel; D005056:Euglena gracilis / Q000032:analysis*; D015852:Eukaryotic Initiation Factor-2; D046911:Macromolecular Substances; D010448:Peptide Initiation Factors / Q000302:isolation & purification*; D011506:Proteins / Q000302:isolation & purification*; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism; D012358:RNA, Transfer, Met
chemical_list: D015852:Eukaryotic Initiation Factor-2; D046911:Macromolecular Substances; D010448:Peptide Initiation Factors; D011506:Proteins; D012346:RNA, Transfer, Amino Acyl; D012358:RNA, Transfer, Met; C024988:tRNA, formylmethionine-