RPL5(ribosomal protein L5)為真核細胞中組成核糖體60S次體之一員。在真核細胞中，於細胞質被合成出來的核糖蛋白必須回到細胞核內，與在核內轉錄完成的核糖體RNA(ribosomal RNA)於核仁中進行核糖體的組裝，完成之核糖體大、小次體再被送到細胞質中執行其轉譯蛋白質的功能。而細胞內之5S rRNA不像其它rRNA直接在核仁中進行轉錄作用，而是在核質中轉錄出，因此它便需要藉由與核糖蛋白L5形成5S rRNP複合物之型態，讓L5將其攜帶至核仁中進行核糖體之組合。
細胞內大約只有一半的L5蛋白存在於核糖體中，有一半則與5S rRNA結合形成5S rRNP存在核中，除了具有運送5S rRNA之功能外，過去研究報告顯示L5亦能和細胞內一些其他蛋白質結合，如：去磷酸酶(typeⅠphosphatase)、激酶蛋白CKⅡ並受其磷酸化、以及致癌蛋白mdm2，而可形成5S RNA-L5-mdm2-p53核糖蛋白複合物，因此L5可能參與了其它細胞內之調控作用。
之前有研究報告指出RPA2之磷酸化可能使p53由RPA-p53複合物中釋出而導致了p53的活化以及L5會與mdm2和mdm2-p53的複合物結合。我們實驗室先前的研究發現當細胞經由UV照射後，L5會與磷酸化的RPA2交互作用。就之前研究結果，我們想了解L5是否直接與p53結合而參與p53的活化機制，進而調控了DNA的代謝，影響了細胞的週期。因此我們利用TNT in vitro transcription/translation system kit將標定上35S同位素的L5和p53蛋白表現出來，再以免疫沉澱法來偵測此兩蛋白是否有直接的交互作用。實驗結果顯示，L5與p53蛋白間的確有交互作用，接下來我們進一步想了解L5是結合在p53的哪個區域，首先進行p53的截斷，然後分別構築到pET21質體上，還是利用TNT in vitro transcription/translation system kit與免疫沉澱法去偵測交互作用的情形，實驗結果顯示，L5可能是結合在p53的C端。
Klebsiella pneumoniae 是引起社區型及院內嚴重症狀感染常見之病原菌，並有高致病力。特殊的是K. pneumoniae 是台灣地區引起化膿性肝膿瘍最重要的致病菌，其發生率之高亦是世界其它地區所無法相比，也因此所以促使我們去研究K. pneumoniae 的致病因子。之前本實驗室由K. pneumoniae (K.p.129)基因庫中找到一個疑為致病因子的外膜蛋白-2(OMP-2)，直接以動物實驗觀察在主動及被動免疫的保護效果，在主動免疫方面可達90%，被動免疫為70%，且在基因保留性的探討中，發現在其它K. pneumoniae 菌株中都可夾出外膜蛋白的共同保留區，推測這保留區應在致病機轉上扮演重要的角色。所以我們想進一步了解外膜蛋白-2是否為K.p.129主要的致病因子，因此我們以同源重組的原理，改變野生株K.p.129染色體上保留區間的外膜蛋白基因而獲得突變株，並由PCR及Southern blot的結果確認無誤後，再接著以BALB/CJ小鼠測試突變株與野生株半致死率(LD50)的差異，由實驗結果顯示，突變株與野生株的半致死率並無差異，可見外膜蛋白-2可能不是K.p.129主要的致病因子。

L5 is an 894bp, 34KDa ribosomal protein that is a part of 60S ribosomal subunit and localizes in both the cytoplasm and the nucleus of eukaryotic cells, accumulating particularly in the nucleoli. L5 is known to bind specifically to 5S rRNA and is involved in nucleocytoplasmic transport of this rRNA. In mammalian cells,only about half of the L5 are in 60S ribosome and the other half of the L5 are bound by 5S rRNA to form an 5S RNP in the nucleus. L5 can also be associated with type Ⅰphosphatase, CKⅡ (casein kinase Ⅱ) and oncoprotein mdm2. L5 may be involved in other intracellular regulatory mechanism.
Previous reports indicated that phosphorylation of RPA2 prevents the association of RPA with p53 , and L5 is associated with mdm2 and mdm2-p53 complexes. Also, in our previous study, we discovered that L5 interactes with hyperphosphorylated form of RPA2, but not with hypophorylated form of RPA2, when cells was irradiated with UV. This raises an interesting possibility that L5 might directly associate with p53 in unirradiated cells, and upon UV irradiation, it releases the bound p53, thus transducing the damage signal and activating the p53-dependent checkpoint control. To test this hypothesis, S35-radiolabled L5 and p53 proteins were prepared by coupled in vitro transcription / translation and were subjected to immunoprecipitation analysis with anti-6Histidine antibody. The results showed that L5 can associate with p53 directly. Further study to determine which domain of p53 for L5 binding was proceeded. The results revealed that L5 can bind at the carboxyl terminus of the p53 protein.
Klebsiella pneumoniae is the common pathogen of nosocomial and community-acquired infections, especially bacterium, pneumonia, and urinary tract infections. In Taiwan, the high incidence of K. pneumoniae pyogenic liver abscess has been reported which never reported in English literature during the period from 1980 (30%) to 1990 (82.1%). The exact mechanisms of increasing incidence of K. neumoniae pyogenic liver abscess in Taiwan is unclear. In our previous study, a gene encoding outer membrane protein(OMP2) has been cloned from a highly virulent strain of K.p.129 ( LD50 < 102 c.f.u.), and anti-OMP2 antibody has a significantly protective effect when administered before acute lethal infection. Thus, correlation of OMP2 with respect to the virulence of K. pneumoniae was examinied in this study. Several isogenic OMP2-deficient strains were constructed by using integrational plasmid to disrupt the omp2 gene. The deficient strains checked by PCR and southern blotting, which was further examined by LD50 test. The results indicate that OMP2 may be not play a more important role in the pathogenesis of K. pneumoniae.

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