Human fetal hemoglobin synthesis and its NH2-terminal acetylation in a rabbit reticulocyte lysate translational system.

The biosynthesis of the acetylated (Hb FIc) and the non-acetylated (Hb F0) human fetal hemoglobin components has been examined in a cell-free translational system. The poly(A)-RNA was isolated from umbilical cord blood samples and translated in the heterologous translational system derived from rabbit reticulocyte lysates in the presence of labeled amino acid(s) or acetyl-CoA. The amount of each hemoglobin or globin chain made in the system was determined by separating the synthesis products by cation-exchange chromatographic methods. The in vitro synthesis ratios were close to the FIc/Ftotal values of the respective hemolysates. The same conclusion could be reached by determining the specific activity ratios of Hb FIc/Hb F0. Co-migration of radioactivity peaks with absorbance peaks indicated the synthesis of that hemoglobin or globin chain. Confirmation of the synthesis of true gamma 0 and gamma Ic was accomplished by high-pressure liquid chromatographic separation of 3H-labeled tryptic peptides. Each peptide corresponded well with the radioactivity peak. Labeled acetyl-group incorporation into Hb FIc and gamma IcT-1 provided direct evidence for acetylation of gamma chains in Hb FIc. The data indicate that the mRNA itself dictates whether a protein is acetylated and, if so, to what extent. The control appears to be not unique to the human red cell system.