  To test whether X-chromosome has unique genomic characteristics, X-chromosome
and 22 autosomes were compared for RNA binding density. Nucleotide sequences on
the chromosomes were divided into 50kb per segment that was recoded as a set of
frequency values of 7-nucleotide (7nt) strings using all possible 7nt strings
(47=16384). 120 genes highly expressed in tonsil germinal center B cells were
selected for calculating 7nt string frequency values of all introns (RNAs). The
binding density of DNA segments and RNAs was determined by the amount of
complement sequences. It was shown for the first time that gene-poor and low
gene expression X-chromosome had the lowest percentage of the DNA segments that
can highly bind RNAs, whereas gene-rich and high gene expression chromosome 19
had the highest percentage of the segments. On the basis of these results, it
is proposed that the nonrandom properties of distribution of RNA highly binding
DNA segments on the chromosomes provide strong evidence that lack of RNA highly
binding segments may be a cause of X-chromosome inactivation
