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 findings about preferential 
positioning of splice junctions within the nucleosomes. The RR and YY 
dinucleotides oscillate counter-phase, i.e., their respective preferred 
positions are shifted about half-period from one another, as it was observed 
earlier for AA and TT dinucleotides. Species specificity of nucleosome 
positioning DNA pattern is indicated by the 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.