Genes for stable RNA in the extreme thermophile Thermoproteus tenax: introns and transcription signals
Genes for stable RNA in the extreme thermophile Thermoproteus tenax: introns and transcription signals
复制标题
极端嗜热菌 Thermoproteus tenax 中稳定 RNA 的基因：内含子和转录信号
作者：
G. Wich;W. Leinfelder;A. Böck
为了研究极端嗜热古细菌的基因组织和表达信号，从 Thermoproteus tenax 中克隆了 tRNA 基因。获得了五种 tRNA 的克隆，即 tRNAAla (TGC)、tRNAAla (CGC)、tRNALeu (CAG)、tRNALeu (CAA) 和 tRNAMet (CAT)。三个各自的基因单独位于染色体中，另外两个（tRNAAla 和 tRNAMet）聚集在一起，但处于头对头的位置。其中四个基因包含插入序列，或者位于反密码子的经典位置 3' (tRNAMet)，或者位于反密码子序列 (tRNALeu CAG) 内，或者位于反密码子干区 (tRNAAla) 内迄今为止唯一的反密码子位置 5'。核酸酶 S1 作图证明了包含插入序列的转录物的存在。所有 tRNA 基因的螺旋区 G-C 碱基对都极其丰富，这一特征可能有助于二级结构的热稳定性。通过核酸酶 S1 作图确定 Thermoproteus 的 16S/23S rRNA 操纵子和两个 tRNA 基因的转录起始位点。 tRNA 基因的转录起始于结构基因的 5' 端附近或紧邻结构基因的 5' 端，即编码区上游 175 bp 的 rRNA 操纵子的 5' 端。转录起始位点上游约 18 bp 处，富含 AT 的保守序列基序出现在相当富含 GC 的顺反子间间隔区内。假定其在 Thermoproteus 的高生长温度下不稳定性表明其具有作为 RNA 聚合酶进入位点的功能。
To investigate gene organization and expression signals in extreme thermophilic archaebacteria, tRNA genes were cloned from Thermoproteus tenax. Clones for five tRNA species were obtained, namely for tRNAAla (TGC), tRNAAla (CGC), tRNALeu (CAG), tRNALeu (CAA) and tRNAMet (CAT). Three of the respective genes were located singly in the chromosome, the two others (tRNAAla and tRNAMet) were clustered but in a head to head position. Four of the genes contained intervening sequences, either in the classical position 3′ to the anticodon (tRNAMet), or within the anticodon sequence (tRNALeu CAG), or in the hitherto unique position 5′ to the anticodon within the anticodon stem region (tRNAAla). Existence of a transcript containing the intervening sequence was demonstrated by nuclease S1 mapping. All tRNA genes were extremely rich in G–C basepairs of helical regions, a feature which may contribute to thermostability of the secondary structure. The start site of transcription of the 16S/23S rRNA operon and of two tRNA genes of Thermoproteus was determined by nuclease S1 mapping. Transcription of the tRNA genes initiates close to or immediately at the 5′ end of the structural gene, that of the rRNA operon 175 bp upstream of the coding region. About 18 bp upstream of the transcription initiation site a conserved AT‐rich sequence motif occurs within a fairly GC‐rich intercistronic spacer. Its putative instability at the high growth temperature of Thermoproteus suggests a function as entry site for RNA polymerase.