CLONING AND CHARACTERIZATION OF RIBOSOMAL-RNA GENES FROM WHEAT AND BARLEY

Wheat and barley DNA enriched for ribosomal RNA genes was isolated from actinomycin D-CsCl gradients and used to clone the ribosomal repeating units in the plasraid pAC184. All five chimeric plasmids Isolated which contained wheat rDNA and eleven of the thirteen which had barley rDNA were stable and included full length ribosomal repeating units.Physical maps of all length variants cloned have been constructed using the restriction endonucleases Eco Rl, Bam H1, Bgl II, Hind III and Sal I. Length variation 1n the repeat units was attributed to differences 1n the spacer regions. Comparison of Hae III and Hpa II digestion of cereal rDNAs and the cloned repeats suggests that most methylated cytosines in natural rONA are in -CpG-. Incomplete methylation occurs at specific Bam HI sites in barley DNA. Detectable quantities of ribosomal spacer sequences are not present at any genomic locations other than those of the ribosomal RNA gene repeats. © 1979 Information Retrieval Limited.