Gene enrichment using antibodies to DNA/RNA hybrids: purification and mapping of Dictyostelium discoideum rDNA.

Antibodies, shown to be specific for DNA/RNA hybrids, have been covalently attached to CNBr-activated Sepharose. The resultant affinity resin specifically binds DNA/RNA hybrids and has been used to enrich for the DNA which codes for rRNA in the slime mold Dictyostelium discoideum. By utilizing the technique of R-loop formation, DNA molecules containing the rRNA genes were isolated from total nuclear DNA in a double-stranded form. These rDNA molecules, which were recovered by high salt elution from the affinity resin, were typically 15-40 kbp in length, and thus contained DNA sequences adjacent to the selected sequences coding for the 17S and 26S rRNAs. In addition, evidence has been obtained concerning the structure of Dictyostelium rDNA which agrees with the finding (Taylor et al. (1977) ICN-UCLA Symp. Mol. Cell. Biol. 8, 309-313) that the rDNA molecules are not covalently attached to the chromosomes of this organism.