Ohnishi M, Janosi L, Shuda M, Matsumoto H, Hayashi T, Terawaki Y, Kaji A
Department of Bacteriology, Shinshu University School of Medicine, Matsumoto, Nagano-Ken 390-8621, Japan.
J Bacteriol. 1999 Feb;181(4):1281-91. doi: 10.1128/JB.181.4.1281-1291.1999.
Ribosome recycling factor (RRF) is required for release of 70S ribosomes from mRNA on reaching the termination codon for the next cycle of protein synthesis. The RRF-encoding gene (frr) of Pseudomonas aeruginosa PAO1 was functionally cloned by using a temperature-sensitive frr mutant of Escherichia coli and sequenced. The P. aeruginosa frr was mapped at 30 to 32 min of the P. aeruginosa chromosome. The deduced amino acid sequence of RRF showed a 64% identity to that of E. coli RRF. In an assay including E. coli polysome and elongation factor G, purified recombinant RRF of P. aeruginosa released monosomes from polysomes. This is the first case in which an RRF homologue was found to be active in heterogeneous ribosome recycling machinery. The genes for ribosomal protein S2 (rpsB), elongation factor Ts (tsf), and UMP kinase (pyrH) are located upstream of frr. The arrangement of the genes, rpsB-tsf-pyrH-frr, resembles those reported for E. coli and Bacillus subtilis. Even in the cyanobacterium genome, the arrangement pyrH-frr is conserved. Although RRF homologues are found in eukaryotic cells, phylogenetic analysis suggests that they were originally present within the members of the phylogenetic tree of prokaryotic RRF. This finding suggests that the ribosome recycling step catalyzed by RRF is specific for prokaryotic cells and that eukaryotic RRF is required for protein synthesis in organelles, which are believed to be phylogenetically originated from prokaryotes.
核糖体循环因子（RRF）是在下一轮蛋白质合成到达终止密码子后，使70S核糖体从mRNA上释放所必需的。通过使用大肠杆菌的温度敏感型frr突变体，对铜绿假单胞菌PAO1的RRF编码基因（frr）进行了功能克隆并测序。铜绿假单胞菌的frr基因定位于铜绿假单胞菌染色体的30至32分钟处。推导的RRF氨基酸序列与大肠杆菌RRF的氨基酸序列具有64%的同一性。在一项包含大肠杆菌多核糖体和延伸因子G的测定中，纯化的铜绿假单胞菌重组RRF从多核糖体中释放出单核糖体。这是首次发现RRF同源物在异源核糖体循环机制中具有活性。核糖体蛋白S2（rpsB）、延伸因子Ts（tsf）和UMP激酶（pyrH）的基因位于frr的上游。基因rpsB-tsf-pyrH-frr的排列类似于大肠杆菌和枯草芽孢杆菌中报道的排列。即使在蓝藻基因组中，pyrH-frr的排列也是保守的。尽管在真核细胞中发现了RRF同源物，但系统发育分析表明它们最初存在于原核RRF系统发育树的成员中。这一发现表明，由RRF催化的核糖体循环步骤对原核细胞具有特异性，而真核RRF是细胞器中蛋白质合成所必需的，细胞器被认为在系统发育上起源于原核生物。
