Molecular and physical organization of highly repetitive, undermethylated DNA from Pennisetum glaucum

A HaeIII monomer of a repetitive DNA family from Pennisetum glaucum (L.) R. Br. cv. Massue has been cloned and characterized. The repeat is 137 bp long and is organized in head-to-tail orientation in tandem arrays. The HaeIII monomer contains 55% A+T residues. The distribution of this highly repetitive sequence in different Pennisetum species and in other cereals was investigated. The HaeIII satellite is present in all Pennisetum species investigated but absent from other genera examined. In situ hybridization revealed a centromeric localization of this sequence on all seven chromosome pairs and indicated chromosome-specific differences in copy number. Methylation was investigated by comparative restriction enzyme analysis (MspI/HpaII) which showed a greater extent of methylation of the internal C of the enzyme recognition site 5'-CCGG. A South-Western analysis, using an anti-methylcytosine antibody to examine the methylation status in P. glaucum confirmed that the sequence is not highly methylated.