Transcription signals for stable RNA genes in Methanococcus.
Transcription signals for stable RNA genes in Methanococcus.
复制标题
甲烷球菌中稳定 RNA 基因的转录信号。
作者：
G. Wich;H. Hummel;M. Jarsch;U. Bär;A. Böck
先前对古细菌凡尼氏甲烷球菌 tRNA 基因上游序列的调查显示，存在两个序列同源性框：框“A”，包含约 20 个保守核苷酸，距基因上游 30 至 49 个碱基对，框“B”，框“A”下游 18 至 19 个核苷酸（Wich, G.、Sibold, L. 和 Böck, A. (1985) 应用微生物学 (Nuclease S1) 进行图谱实验，利用这些 tRNA 转录单位和核糖体 RNA 操纵子，利用来自甲烷球菌的细胞在蛋白质合成抑制的条件下积累初级转录物和加工核糖体 RNA 的中间体这一事实，获得了以下结果：由于框“B”基序 5'TGCaagT3' 也出现在产甲烷生物和嗜盐生物中蛋白质编码基因的转录起始位点，因此它似乎构成了这些古细菌群中常用的转录起始信号（ii）框“A”基序相对于框“B”以恒定的间距出现在所有 10 种 tRNA 和核糖体 RNA 中。由于它不存在于编码蛋白质的基因的前导区域中，因此它似乎充当稳定 RNA 基因表达所需的特定元件。研究的甲烷球菌菌株中稳定 RNA 基因的终止信号似乎与真核生物中稳定 RNA 基因的终止信号相似 (iv) 通过核酸酶 S1 定位，鉴定了参与前核糖体 RNA 成熟的加工酶。
A previous survey of upstream sequences of tRNA genes from the archaebacterium Methanococcus vannielii has revealed that there are two boxes of sequence homology: A box "A" of about 20 conserved nucleotides at a distance of 30 to 49 basepairs upstream from the gene and a box "B" 18 to 19 nucleotides downstream from box "A" (Wich, G., Sibold, L., and Böck, A. (1985) System. Appl. Microbiol. (in press). Nuclease S1 mapping experiments were carried out with two of these tRNA transcriptional units and with a ribosomal RNA operon, to determine whether these consensus sequences have a function in the initiation of transcription. Use was made of the fact that cells from Methanococcus accumulate primary transcript and processing intermediates of ribosomal RNA under conditions of protein synthesis inhibition. The following results were obtained: (i) Transcription in all three systems starts at the G within the conserved trinucleotide TGC of box "B". Since the box "B" motif, 5'TGCaagT3', also occurs at the site of transcription initiation of protein encoding genes, both in methanogenic and halophilic organisms, it appears to constitute a frequently used transcription start signal within these archaebacterial groups. (ii) The box "A" motif occurs with constant spacing, relative to box "B", in all 10 tRNA and ribosomal RNA transcriptional units investigated from Methanococcus. Since it is not present in the leader region of genes coding for proteins, it seems to function as a specific element which is required for the expression of genes for stable RNA. (iii) Termination of transcription of the ribosomal RNA operon from Methanococcus occurs at a distinct T within an oligo-T stretch immediately downstream from the 3'-terminal 5S RNA gene. This signal occurs in all 3'-flanking regions of transcriptional units for stable RNA from the Methanococcus strains studied. Termination signals for stable RNA genes in Methanococcus appear to be similar with those of stable RNA genes in eukaryotes. (iv) By nuclease S1 mapping a recognition site was identified for a processing enzyme involved in the maturation of preribosomal RNA.