Involvement of polypurine and polypyrimidine nucleotide sequences of DNA in
compactization of gene chromosomal domains was analyzed. Tracts (10 bp or
longer) of purines and pyrimidines potentially able to interact forming tri
pler structures ("structurizing regions" of chromosomal domains of the gene
s) were found in introns and at the flanks of three animal and two plant ge
nes. If DNA-DNA interactions are the same in vivo, the chromosomal loci of
eukaryotic genes could be compacted in several small loops. These interacti
ons within a small region should result in formation of rosette-like struct
ures. Clustering of the "structurizing regions" in chromosomal loci of the
genes may be of functional importance.