RNA Binding Density on X-chromosome Differing from that on 22 Autosomes in Human

Abstract: 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