CAJ | 학술논문

X染色体发生X染色体失活,但是Xp基因有30%表现为逃逸,而Xq仅不到3%.为了研究X染色体基因失活和表达逃逸发生和维持的分子机制,比较了Xq和Xp DNA序列的RNA模拟结合强度.X染色体的核苷酸序列被分为50 kb一段, 对每一段DNA做7碱基(7 nt)字符串组合分析(共有47=16 384种组合),记录每段50 kb DNA中每种7 nt字符串的频率.选择生发中心B细胞中的120个高表达基因,计算这些基因的内含子7 nt字符串的出现频率,称为intron 7nt,以此作为RNAs(RNA群,模拟细胞中RNA在小片段的总和).已知一段DNA序列的7 nt频率值和intron 7nt,即可以计算该DNA段与intron 7nt的结合强度.每段50 kb DNA与intron 7nt的结合强度取决于该DNA段与intron 7nt互补核苷酸的频率,互补的核苷酸序列越多,结合强度就越大.DNA段与intron 7nt 的模拟结合强度称为RNA结合强度,试图模拟该段DNA可以结合的RNA小片段的总量.之所以采用7 nt字符串组合分析是考虑到连续7个核苷酸互补则可以形成相对稳定的结合.研究发现:1)Xp各DNA段的RNA结合强度均值显著大于Xq (P<0.001);2)Xp上高结合RNA的DNA段数目显著高于Xq (P<0.001); 3) RNA高结合DNA段形成的簇与X染色体基因表达逃逸区关联.有证据表明,RNA可以通过改变染色质构象活化基因并且该作用具有普遍意义:如RNA增加染色质对DNaseⅠ消化的敏感性,互补RNA-DNA的亲和性高于互补DNA-DNA,细胞中有丰富的非编码RNA和非编码DNA等.研究中的发现结合RNA活化基因的观点,提示Xp逃逸失活基因的数目多于Xq可能与前者的RNA结合强度大于后者有关.
X염색체발생X염색체실활,단시Xp기인유30%표현위도일,이Xq부불도3%.위료연구X염색체기인실활화표체도일발생화유지적분자궤제,비교료Xq화Xp DNA서렬적RNA모의결합강도.X염색체적핵감산서렬피분위50 kb일단, 대매일단DNA주7감기(7 nt)자부천조합분석(공유47=16 384충조합),기록매단50 kb DNA중매충7 nt자부천적빈솔.선택생발중심B세포중적120개고표체기인,계산저사기인적내함자7 nt자부천적출현빈솔,칭위intron 7nt,이차작위RNAs(RNA군,모의세포중RNA재소편단적총화).이지일단DNA서렬적7 nt빈솔치화intron 7nt,즉가이계산해DNA단여intron 7nt적결합강도.매단50 kb DNA여intron 7nt적결합강도취결우해DNA단여intron 7nt호보핵감산적빈솔,호보적핵감산서렬월다,결합강도취월대.DNA단여intron 7nt 적모의결합강도칭위RNA결합강도,시도모의해단DNA가이결합적RNA소편단적총량.지소이채용7 nt자부천조합분석시고필도련속7개핵감산호보칙가이형성상대은정적결합.연구발현:1)Xp각DNA단적RNA결합강도균치현저대우Xq (P<0.001);2)Xp상고결합RNA적DNA단수목현저고우Xq (P<0.001); 3) RNA고결합DNA단형성적족여X염색체기인표체도일구관련.유증거표명,RNA가이통과개변염색질구상활화기인병차해작용구유보편의의:여RNA증가염색질대DNaseⅠ소화적민감성,호보RNA-DNA적친화성고우호보DNA-DNA,세포중유봉부적비편마RNA화비편마DNA등.연구중적발현결합RNA활화기인적관점,제시Xp도일실활기인적수목다우Xq가능여전자적RNA결합강도대우후자유관.
30% of the genes tested on Xp escaped inactivation,whereas less than 3% of the genes on Xq escaped inactivation.To investigate the molecular mechanism involved in the propagation and maintenance of X chromosome inactivation and escape,the long arm and short arm of the X chromosome were compared for RNA binding density.Nucleotide sequences on the X chromosome were divided into 50 kb per segment that was recorded as a set of frequency values of 7-nucleotide (7 nt) strings using all possible 7 nt strings (47=16 384).120 genes highly expressed in the tonsil germinal center B cells were selected for calculating the 7 nt string frequency values of all introns (intron 7nt).Intron 7nt was considered RNAs (RNA population) that simulated the total of small RNA fragments in cells.Knowing the 7 nt frequency values of DNA segments and the intron 7nt,we can calculate the binding density of DNA segments to the intron 7nt that was termed as RNA binding density.The RNA binding density was determined by the amount of complement sequences.The more amount of complement sequences,the more density of RNA binding.The RNA binding density simulated the total of small RNA fragments bound to the DNA segment.Several principal characteristics were observed for the first time: (1) The mean value of RNA binding density of DNA segments on Xp was significantly higher than that on Xq (P<0.001); (2) The numbers of DNA segments highly binding RNAs were more on Xp than on Xq (P<0.001); (3) The clusters of RNA highly binding DNA segments were associated with regions in which genes escape inactivation.It has been suggested that RNAs activate genes and the interaction of RNA-DNA in cells are extensive,for example,RNAs increase DNaseⅠsensitivity of DNA,there is plenty of nonprotein-coding RNAs in cells,the binding specificity of DNA-RNA is far higher than that of DNA-protein and the affinity of DNA with RNA is increased,as compared with DNA.The nonrandom properties of distribution of RNA highly binding segments between Xp and Xq,combined with the finding of RNA activating genes,provide a strong evidence that RNA highly binding segments may serve as DNA signals to propagate activation along a chromosome and vice versa,the DNA segments that less bind RNAs may silence the genes.