Abstracts Biological Sciences

Isolation and characterization of messenger ribonucleic acid for hemoglobin

by David Gerald Laycock

Typescript. Bibliography: leaves 109-114. viii, 114 l illus An 8s ribonucleic acid (RNA) species, isolated from rabbit reticulocytes, has been purified by salt fractionation and analyzed for characteristics of an information-carrying, messenger RNA. This RNA in reticulocytes is restricted to polyribosome complexes which are active in hemoglobin synthesis and has a base composition similar to that expected of a messenger RNA for rabbit globin. This RNA species has been assayed for the ability to support and direct protein synthesis in bacterial extracts. The 8s RNA from reticulocyte polyribosomes is translated when only N-acetyl-valyl- tRNA is present as an initiation residue. Both rabbit globin polypeptide chains have N-terminal valine residues. The protein produced in bacterial extracts directed by this RNA is identical to rabbit globin by chromatography on diethylaminoethyl-cellulose, carboxymethyl-Sephadex C50, paper electrophoresis and gel-filtration on Sephadex G75. The protein product combines with added hemin and the resultant complex is indistinguishable from native rabbit hemoglobin by the above criteria. The profile of tryptic peptides from chromatography on Dowex 50x2 indicates the product is N-acetyl globin. The implications of these results concerning the universality of the genetic code and of protein biosynthetic mechanisms at a macromolecular level are discussed.