Hemoglobin switching in sheep and goats. Preparation and characterization of complementary DNAs specific for the alpha-, beta-, and gamma-globin messenger RNAs of sheep.

Specific complementary DNAs (cDNAs) for the messenger RNAs coding for sheep alpha-, betaA-, betaB-, betaC-, and gamma-globins were prepared by thermal denaturation of heterologous hybrids (e.g. alphabetaB-cDNA-alphagamma-mRNA) followed by hydroxylapatite chromatography. Each cDNA represented a nearly full-length copy of its globin mRNA complement as determined by electrophoretic analysis in polyacrylamide gels containing 98% formamide. The purity of each cDNA fraction was estimated by hybridization analysis and thermal denaturation. The beta- and gamma-cDNAs contained 5 to 20% contaminating alpha-cDNA while the alpha-cDNA was 25 to 30% contaminated with non-alpha-cDNA. The melting temperatures (Tm) of homologous duplexes between each non-alpha chain cDNA and its mRNA complement ranged from 69.5-71.5 degrees in 50% formamide while alpha-alpha duplexes melted with a Tm of 75-76 degrees. The Tm values of heterologous duplexes formed between each non-alpha-cDNA and the various globin mRNAs (e.g. betaB-cDNA-Hb C mRNA) ranged between 64.5 degrees and 68 degrees and thus were only 1.5-5.0degrees below that of homologous duplexes. These results suggest that the nucleotide sequence divergence among the various non-alpha-mRNAs (or cDNAs) is not greatly different from the minimum predicted from the amino acid sequence differences of the corresponding globins. When annealing reactions were performed above the Tm of the heterologous hybrids (68 degrees), each non-alpha-cDNA hybridized only to its own complementary mRNA. Thus the purified cDNAs provide molecular probes for the quantitation of alpha-, beta-, and gamma-globin-specific nucleotide sequences.