Ribosomal RNA genes in Kluyveromyces marxianus

DNA from the yeast Kluyveromyces marxianus was studied for its heterogeneity and the multiplicity of rRNA cistrons. These cistrons banded at a slightly different density from the bulk DNA in preparative CsCl or Hg2+-Cs2SO4 equilibrium density gradients. The reassociation kinetics of the bulk DNA showed that the repetitive fraction represented a small amount of the total cellular DNA (10%) and that the single copy fraction had a complexity of 6.3 X 10(9) daltons. Approximately 2.2% of the DNA hybridized to 3H-labelled rRNA at saturation. On the basis of the above genome size, the multiplicity of the rRNA cistrons was calculated to be about 70 per haploid nucleus.