Jovanovic G, Model P
Laboratory of Genetics, Rockefeller University, New York 10021, USA.
J Bacteriol. 1997 May;179(10):3095-102. doi: 10.1128/jb.179.10.3095-3102.1997.
The sequence (2,700 bp) between the aldH and pspF genes of Escherichia coli was determined. The pspF gene encodes a sigma54 transcriptional activator of the phage shock protein (psp) operon (pspA to pspE). Downstream of the pspF transcribed region are two open reading frames (ORFs), ordL and goaG, convergently oriented with respect to pspF. These two ORFs, together with the adjacent aldH gene, may constitute a novel operon (aldH-ordL-goaG). The goaG-pspF intergenic region contains a complex extragenic mosaic element, RIB. The structure of this RIB element, which belongs to the BIME-1 family, is Y(REP1) > 16 < Z1(REP2), where Y and Z1 are palindromic units and the central 16 bases contain an L motif with an ihf consensus sequence. DNA fragments containing the L motif of the psp RIB element effectively bind integration host factor (IHF), while the Y palindromic unit (REP1) of the same RIB element binds DNA gyrase weakly. Computer prediction of the pspF mRNA secondary structure suggested that the transcribed stem-loop structures formed by the 3'-flanking region of the pspF transcript containing the RIB element can stabilize and protect pspF mRNA. Analysis of pspF steady-state mRNA levels showed that transcripts with an intact RIB element are much more abundant than those truncated at the 3' end by deletion of either the entire RIB element or a single Z1 sequence (REP2). Thus, the pspF 3'-flanking region containing the RIB element has an important role in the stabilization of the pspF transcript.
测定了大肠杆菌aldH基因和pspF基因之间的序列（2700 bp）。pspF基因编码噬菌体休克蛋白（psp）操纵子（pspA至pspE）的σ54转录激活因子。在pspF转录区域的下游有两个开放阅读框（ORF），即ordL和goaG，它们相对于pspF呈反向排列。这两个开放阅读框，连同相邻的aldH基因，可能构成一个新的操纵子（aldH-ordL-goaG）。goaG-pspF基因间区域包含一个复杂的基因外镶嵌元件RIB。这个属于BIME-1家族的RIB元件的结构是Y(REP1) > 16 < Z1(REP2)，其中Y和Z1是回文单元，中间的16个碱基包含一个带有整合宿主因子（IHF）共有序列的L基序。含有psp RIB元件L基序的DNA片段能有效结合整合宿主因子（IHF），而同一RIB元件的Y回文单元（REP1）与DNA促旋酶的结合较弱。对pspF mRNA二级结构的计算机预测表明，由包含RIB元件的pspF转录本的3'侧翼区域形成的转录茎环结构可以稳定和保护pspF mRNA。对pspF稳态mRNA水平的分析表明，具有完整RIB元件的转录本比那些通过删除整个RIB元件或单个Z1序列（REP2）而在3'端被截断的转录本丰富得多。因此，包含RIB元件的pspF 3'侧翼区域在稳定pspF转录本方面具有重要作用。
