Preparation and properties of a Met-tRNAf binding factor from rat liver and rat hepatoma

A Met-tRNAf binding factor (IF-2) from the microsomal fraction of rat liver and rat hepatoma ascites cells was partially purified by ammonium sulphate fractionation, DEAE-cellulose and phosphocellulose chromatography. The factor binds [3H]Met-tRNAf only in the presence of either GTP or GMPPCP. Maximal binding takes place at 37 degrees C and in the absence of Mg++. The factor is specific for Met-tRNAf and does not bind Phe-tRNA from rat liver or from E. coli. The ternary complex [Met-tRNAf . IF-2 . GTP1 binds to 40 S ribosomal subunits from rat liver in the absence of mRNA or poly(A, G, U) without GTP hydrolysis. GDP as well as aurintricarboxylic acid inhibit the ternary complex formation. Both factors are rapidly inactivated by N-ethylmaleimide treatment and by preincubation at 45 degrees C. Heat inactivation is partially prevented by GTP and GDP. With regard to the functional properties there are no significant differences between IF-2 from normal liver and hepatoma cells. On the other hand heat denaturation compared to the rat liver factor, which may be due to differences in contaminating proteins.