Chromatin organization and methylation patterns of wheat 5 S RNA genes (Triticum aestivum var. hardi)

The organization of 5 S rRNA genes was examined in the wheat, Triticum aestivum var. Hardi, and three size classes of repeated units were recognized. Digestion with micrococcal nuclease of nuclei from ungerminated embryos or from embryos germinated for 48 h revealed that these tissues have 5 S genes organized into nucleosomes with repeat lengths similar to those of bulk chromatin. No special arrangement of nucleosomes with respect to 5 S DNA sequences was found. The 5 S DNA methylation pattern was determined in genomic DNA at both developmental stages. The 410 bp unit family has significant undermethylation at CCGG sites, in both active and inactive tissues. This is in marked contrast to the situation with the 500 bp unit family, which has nearly all CCGG sites methylated at both developmental stages.