COMPARATIVE-ANALYSIS OF THE NUCLEOSOMAL STRUCTURE OF RYE, WHEAT AND THEIR RELATIVES

Analysis of the structure of chromatin in cereal species using microco ccal nuclease (MNase) cleavage showed nucleosomal organization and a l adder with typical nucleosomal spacing of 175-185 bp. Probing with a s et of DNA probes localized in the authentic telomeres, subtelomeric re gions and bulk chromatin revealed that these chromosomal regions have nucleosomal organization but differ in size of nucleosomes and rate of cleavage between both species and regions. Chromatin from Secale and Dasypyrum cleaved more quickly than that from wheat and barley, perhap s because of their higher content of repetitive sequences with hairpin structures accessible to MNase cleavage. In all species, the telomeri c chromatin showed more rapid cleavage kinetics and a shorter nucleoso me length (160 bp spacing) than bulk chromatin. Rye telomeric repeat a rrays were shortest, ranging from 8 kb to 50 kb while those of wheat r anged from 15 kb up to 175 kb. A gradient of sensitivity to MNase was detected along rye chromosomes. The rye-specific subtelomeric sequence s pSc200 and pSc250 have nucleosomes of two lengths, those of the telo meric and of bulk nucleosomes, indicating that the telomeric structure may extended into the chromosomes. More proximal sequences common to rye and wheat, the short tandem-repeat pSc119.2 and rDNA sequence pTa7 1, showed longer nucleosomal sizes characteristic of bulk chromatin in both species. A strictly defined spacing arrangement (phasing) of nuc leosomes was demonstrated along arrays of tandem repeats with differen t monomer lengths (118, 350 and 550 bp) by combining MNase and restric tion enzyme digestion.