Bélanger G, Gingras G
Département de Biochimie, Université de Montréal, Québec, Canada.
J Biol Chem. 1988 Jun 5;263(16):7639-45.
In Rhodospirillum rubrum, the genes coding for the alpha and beta polypeptides of the B880 antenna (pufA,B) and the L and M polypeptides of the photoreaction center (pufL,M) are clustered on operon puf. In oxygen-limited cells, the puf mRNA is present as species of 2561, 640, and 617 nucleotides. Aerated cells contain only traces of these mRNAs. The large mRNA encodes the alpha,beta, L, and M polypeptides, whereas the small mRNAs encode only alpha and beta. S1 nuclease protection mapping showed these transcripts to have a common 5' end, immediately downstream of a region of dyad symmetry and at 166 nucleotides upstream of the initiation codon of pufB. The 3' termini of the small transcripts are located in the intercistronic region between pufA and pufL, downstream of another region of dyad symmetry. This region is highly conserved in Rhodospirillum rubrum, Rhodobacter capsulatus, and Rhodobacter sphaeroides and shares 61% sequence similarity with the repetitive extragenic palindromic sequences of Escherichia coli. The slightly heterogeneous 3' termini of the large transcript are downstream of a region of dyad symmetry characteristic of rho-independent transcription termination. Following a shift from oxygen-limited to aerated conditions, the pufL,M and the pufA,B mRNAs decayed with respective half-lives of 9 and 20 min. These high relative stabilities, attributed to secondary structure, are in accord with the mole ratio (2:1) of the pufA,B/pufL,M messages. While the differential expression of alpha,beta/L,M congruent to 15 is thought to be due, in part, to this relative stability, the main factor may be a more efficient translation initiation for pufA,B than for pufL,M.
在深红红螺菌中，编码B880天线的α和β多肽（pufA、B）以及光反应中心的L和M多肽（pufL、M）的基因聚集在操纵子puf上。在氧受限的细胞中，puf mRNA以2561、640和617个核苷酸的种类存在。通气的细胞仅含有这些mRNA的痕量。大的mRNA编码α、β、L和M多肽，而小的mRNA仅编码α和β。S1核酸酶保护图谱显示这些转录本有一个共同的5′末端，紧接在二元对称区域的下游且在pufB起始密码子上游166个核苷酸处。小转录本的3′末端位于pufA和pufL之间的顺反子间区域，在另一个二元对称区域的下游。该区域在深红红螺菌、荚膜红细菌和球形红细菌中高度保守，并且与大肠杆菌的重复基因外回文序列有61%的序列相似性。大转录本稍微异质的3′末端在不依赖ρ的转录终止特征性的二元对称区域的下游。从氧受限条件转变为通气条件后，pufL、M和pufA、B mRNA分别以9分钟和20分钟的半衰期衰减。这些归因于二级结构的高相对稳定性与pufA、B/pufL、M信息的摩尔比（2:1）一致。虽然α、β/L、M≈15的差异表达部分被认为是由于这种相对稳定性，但主要因素可能是pufA、B的翻译起始比pufL、M更有效。
