  Gene sequences in the vicinity of splice sites are found to possess
dinucleotide periodicities, especially RR and YY, with the period close to the
pitch of nucleosome DNA. This confirms previously reported finding about
preferential positioning of splice junctions within the nucleosomes. The RR and
YY dinucleotides oscillate counterphase, i.e., their respective preferred
positions are shifted about half-period one from another, as it was observed
earlier for AA and TT dinucleotides. Species specificity of nucleosome
positioning DNA pattern is indicated by predominant use of the periodical
GG(CC) dinucleotides in human and mouse genes, as opposed to predominant AA(TT)
dinucleotides in Arabidopsis and C.elegans.
  Keywords: chromatin; gene splicing; intron; exon; dinucleotide; periodical
pattern
