Restriction endonuclease analysis of ribosomal DNA from Saccharomyces cerevisiae

Abstract
The size and the degree of homogeneity of the repetitive units in purified ribosomal DNA (γ DNA) from Saccharomyces cerevisiae have been analyzed by restriction endonuclease digestion and heteroduplex mapping. Digestion of the γ DNA with EcoRI yields seven fragments, digestion with Hind II+III yields five fragments, digestion with Hind III alone yields two fragments, and digestion with Sma I yields one fragment. The sum of the fragment molecular weights after digestion with each of the endonucleases is 5.5–5.6×106. When the DNA strands of the Sma I fragment are dissociated and reannealed, only homoduplexes are formed. We have concluded from these results that the repeating units in yeast ribosomal DNA are 5.6×106 daltons and are homogeneous in size and composition.