Qu L H, Meng Q, Zhou H, Chen Y Q
Key Laboratory of Gene Engineering of Education Ministry, Biotechnology Research Center, Zhongshan University, Guangzhou 510275, People's Republic of China.
Nucleic Acids Res. 2001 Apr 1;29(7):1623-30. doi: 10.1093/nar/29.7.1623.
Ten novel small nucleolar RNA (snoRNA) gene clusters, consisting of two or three snoRNA genes, respectively, were identified from Arabidopsis thaliana. Twelve of the 25 snoRNA genes in these clusters are homologous to those of yeast and mammals according to the conserved antisense sequences that guide 2'-O-ribose methylation of rRNA. The remaining 13 snoRNA genes, including two 5.8S rRNA methylation guides, are new genes identified from A.thaliana. Interestingly, seven methylated nucleotides, predicted by novel snoRNAs Z41a-Z46, are methylated neither in yeast nor in vertebrates. Using primer extension at low dNTP concentration the six methylation sites were determined as expected. These snoRNAs were recognized as specific guides for 2'-O:-ribose methylation of plant rRNAs. Z42, however, did not guide the expected methylation of 25S rRNA in our assay. Thus, its function remains to be elucidated. The intergenic spacers of the gene clusters are rich in uridine (up to 40%) and most of them range in size from 35 to 100 nt. Lack of a conserved promoter element in each spacer and the determination of polycistronic transcription from a cluster by RT-PCR assay suggest that the snoRNAs encoded in the clusters are transcribed as a polycistron under an upstream promoter, and individual snoRNAs are released after processing of the precursor. Numerous snoRNA gene clusters identified from A.thaliana and other organisms suggest that the snoRNA gene cluster is an ancient gene organization existing abundantly in plants.
从拟南芥中鉴定出10个新的小核仁RNA（snoRNA）基因簇，分别由两个或三个snoRNA基因组成。根据引导rRNA 2'-O-核糖甲基化的保守反义序列，这些基因簇中的25个snoRNA基因中有12个与酵母和哺乳动物的同源。其余13个snoRNA基因，包括两个5.8S rRNA甲基化引导序列，是从拟南芥中鉴定出的新基因。有趣的是，由新的snoRNAs Z41a-Z46预测的7个甲基化核苷酸在酵母和脊椎动物中均未发生甲基化。在低dNTP浓度下使用引物延伸法，如预期那样确定了6个甲基化位点。这些snoRNAs被认为是植物rRNAs 2'-O-核糖甲基化的特异性引导序列。然而，在我们的实验中，Z42并未引导预期的25S rRNA甲基化。因此，其功能仍有待阐明。基因簇的基因间隔区富含尿苷（高达40%），且大多数间隔区大小在35至100 nt之间。每个间隔区缺乏保守的启动子元件，并且通过RT-PCR分析确定基因簇的多顺反子转录，这表明基因簇中编码的snoRNAs在一个上游启动子的作用下作为多顺反子转录，并且在前体加工后释放出单个的snoRNAs。从拟南芥和其他生物体中鉴定出的大量snoRNA基因簇表明，snoRNA基因簇是一种在植物中大量存在的古老基因组织形式。
