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甲虫着丝粒周围异染色质的转录——卫星DNA作为活跃的调控元件

Transcription of pericentromeric heterochromatin in beetles--satellite DNAs as active regulatory elements.

作者信息

Pezer Z, Ugarković D

机构信息

Department of Molecular Biology, Ruder Bosković Institute, Zagreb, Croatia.

出版信息

Cytogenet Genome Res. 2009;124(3-4):268-76. doi: 10.1159/000218131. Epub 2009 Jun 25.

Abstract

Tenebrionid beetles from the genus Palorus (Coleoptera) have a significant amount of heterochromatin in pericentromeric regions of all chromosomes. The major DNA component of pericentromeric heterochromatin is a highly abundant satellite DNA. Analysis of transcription of a major satellite DNA PSUB from species Palorus subdepressus reveals a constitutive level of expression similar in all 3 developmental stages: larvae, pupae and adults, corresponding to 0.01% of total RNA. Transcription proceeds from both DNA strands in equal amounts resulting in long heterogeneous size transcripts ranging in size from 500 bp to more than 5 kb. Although equal transcription from both DNA strands could potentially activate the RNA interference (RNAi) pathway processing of long PSUB transcripts into small interfering RNAs (siRNA) was not detected. Transcripts preferentially remain in the nucleus and 90% of them are not polyadenylated. Transcription initiation sites, mapped by primer extension, are located within PSUB satellite monomers as well as motifs characteristic for RNA polymerases II and III. Putative RNA polymerase II promoter, predicted by computational approach, shares a 65% sequence similarity to the Pol II promoter mapped previously in PRAT satellite DNA, a major satellite of related species P. ratzeburgii. Results give strong indications that Palorus satellite DNAs are transcribed as autonomous transcription units from their own promoters that reside within satellite sequences. Long satellite DNA transcripts remain mostly in the nucleus and are proposed to play a structural role in the organization of pericentromeric heterochromatin.

摘要

拟谷盗属(鞘翅目)的拟步甲科甲虫在所有染色体的着丝粒周围区域都有大量异染色质。着丝粒周围异染色质的主要DNA成分是一种高度丰富的卫星DNA。对拟谷盗物种的主要卫星DNA PSUB转录情况的分析表明,在幼虫、蛹和成虫这三个发育阶段,其表达水平是组成型的,相当于总RNA的0.01%。转录从两条DNA链等量进行,产生长度各异的长转录本,大小从500 bp到超过5 kb不等。尽管两条DNA链等量转录可能会激活RNA干扰(RNAi)途径,但未检测到长PSUB转录本加工成小干扰RNA(siRNA)。转录本优先留在细胞核中,其中90%没有多聚腺苷酸化。通过引物延伸定位的转录起始位点位于PSUB卫星单体以及RNA聚合酶II和III的特征基序内。通过计算方法预测的推定RNA聚合酶II启动子与先前在PRAT卫星DNA中定位的Pol II启动子有65%的序列相似性,PRAT卫星DNA是相关物种拟谷盗的主要卫星。结果有力地表明,拟谷盗卫星DNA从位于卫星序列内的自身启动子转录为自主转录单元。长卫星DNA转录本大多留在细胞核中,并被认为在着丝粒周围异染色质的组织中起结构作用。

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