摘要或動機

核糖核酸蛋白粒之K 蛋白具有多種功能，可參與在基因轉錄和蛋白質轉譯等過程。我們發現\r
一新奇的cDNA 較已報告的K 蛋白cDNA 少了72 個核?酸，分別命名為S 形與L 形。由基因\r
組DNA 的分析，S 形可能是經由替代剪接少了第8 個exon 所形成。以西方墨點法分析細胞中\r
的K 蛋白，亦證明有S 形存在，其表現量較少且多存在於細胞核中。為了探究兩種K 蛋白等\r
形的表現和功能，我們以PCR 偵測K 蛋白在不同組織與細胞株和人類乳腺腫瘤組織中的RNA\r
表現，結果顯示主要以L 形為主;我們並將S 形與L 形K 蛋白分別轉染至人類乳癌細胞株MCF7\r
中，以抗生素篩選出穩定表現K 蛋白之細胞株，生長速率分析顯示表現S 形之細胞株生長速\r
率較慢，其分子機轉仍有待研究。另外在比對K 蛋白之基因組DNA 時，除了在第九對色體\r
上有完整之K 蛋白基因組DNA，我們亦發現在第2、3、5 及11 對染色體上有類似K 蛋白基\r
因的序列，以cDNA 的形式存在，這些DNA 序列是否可以表現RNA 及其意義為何，目前尚\r
不清楚。Heterogeneous nuclear ribonucleoprotein K (hnRNP K) is a multifunctional protein known to be\r
involved in the regulation of transcription, translation, nuclear transport and signal transduction. We\r
have identified an alternative splicing transcript of hnRNP K lacking exon 8. This novel isoform\r
(named S form compares to L form of full-length hnRNP K) encodes a protein that is 24 amino acids\r
depletion between RNA binding KH1 and KH2 domain. To explore the functional roles of both isoforms,\r
we detect their expression in several tissues (including liver, lung, kidney and heart), cell lines (MCF7,\r
293T, HeLa, NIH3T3, WEHI, P388D1) and specimens of human mammary gland tumor by RT- PCR.\r
The results showed that L form was expressed in all samples, whereas S form was only expressed in cell\r
lines. Using Western blotting analysis, we found that L form existed in both cytosol and nuclear\r
fractions, and little amount of S form was detected in the nuclear extract. Furthermore, we construct the\r
MCF7 cell lines that stably expressed S form or L form hnRNP K. Growth rate analysis indicates that\r
the overexpression of S form of hnRNP K could decrease cell growth rate. The molecular mechanisms\r
of growth inhibition by S form hnRNP K are to be further investigated. On the other hand, when we\r
blast the human genomic genebank, we found except the chromosome 9 containing complete hnRNP K\r
genomic DNA, there are near complete hnRNP K cDNA sequence appears in chromosome 2, 3, 5, and 11.\r
The meaning of these sequences is unclear.