Ovalbumin messenger ribonucleic acid. Purification and fractionation on the basis of polyadenylate content by thermal elution from oligodeoxythymidylate-cellulose.

Ovalbumin messenger RNA was purified from hen oviduct by immunoprecipitation of polysomes and oligo(dT)-cellulose chromatography. Two steps were introduced to improve the separation of mRNA and rRNA by oligo(dT)-cellulose. First, aggregates of mRNA and rRNA were dissociated by heating at 65degrees for 10 min before chromatography. Second, elution of the mRNA was achieved by stepwise increases in temperature rather than by lowering the ionic strength. Ovalbumin mRNA activity was eluted primarily in RNA fractions eluting between 45degrees and 55degrees. Polyacrylamide gel electrophoresis indicated that the ovalbumin mRNA thus obtained was essentiallyyy free of rRNA. The poly(A) content of various thermally eluted fractions was assayed by two methods. In the first (Favre, A., Bertazzoni, V., Berns, A.J.M., and Bloemendal, H. (1974) Biochem. Biophys. Res. Commun. 56, 273-280), the increase in fluorescence intensity of bound ethidium bromide was used to follow the formation of double-stranded RNA during titration of the mRNA with poly(U). In the second (Bishop, J. O., Rosbash, M., and Evans, D. (1974) J. Mol. Biol. 85, 75-86), poly(A) content was derived from the radioactivity remaining acid-insoluble after annealing mRNA fractions with [3H]poly(U) and treating with ribonuclease A. Both methods indicated that ovalbumin mRNA fractions eluting at higher temperatures contained greater amounts of poly(A). Values ranged from 44 to 248 mol of AMP/mol of mRNA, assuming 2200 total nucleotide residues for ovalbumin mRNA (Shapiro, D. J., and Schimke, R. T. (1975) J. Biol. Chem. 250, 1759-1764). Translational specific activities in a rabbit reticulocyte lysate system were essentiall constant for all fractions. From the binding of ethidium bromide it could be estimated that approximately 50% of the nucleotide residues in ovalbumin mRNA are base-paired.