香蕉重泛素基因之選殖與分析

Cloning and Characterization of Polyubiquitin Genes in Banana

本研究選取香蕉基因組選殖系λBUq137進行定序分析。此選殖系包含重泛素基因Mh-UBQ4，演繹之蛋白質具有533個胺基酸，推測分子量為59.7 kDa。Mh-UBQ4具有7個泛素重複單位，頭接尾（head-to-tail）的方式相接，各重複單位中之胺基酸序列有些微差異。以Mh-UBQ4專一性片段為探針進行香蕉各部位北方雜交分析結果，顯示此基因於果肉的表達量高於果皮及其他部位，產生之雜交訊號約1.7 kb。以不同後熟程度分級之香蕉果實，於4℃、15℃、及25℃處理24小時後，進行北方雜交分析結果，4℃處理以第三級果肉表達量最高、25℃處理以第五級果肉表達量較高，而15℃處理則各級果肉表達量相當。 A banana (Musa AAA group Cavendish subgroup) genomic clone λBUQ137 containing polyubiquitin gene Mh-UBQ4 was isolated and analyzed. Mh-UBQ4 encodes a highly conserved 533-amino acid protein with predicted molecular weight of 59.7 kDa. The deduced polypeptide contains seven head-to-tail repeats of ubiquitin and slight difference in amino acid sequence exists among repeats. Using the gene specific fragment as probe, Northern blot analysis indicated that expression level of Mh-UBQ4 transcript, sizing 1.7 kb, was higher in pulp than in other organs. The accumulation of Mh-UBQ4 mRNA in fruit pulp was slightly enhanced by 4℃ and 25℃ incubation for 24 hours for fruits at ripening stage 3 and 5, respectively. When incubated at 15℃ for 24 hours, banana pulps in all ripening stages had similar expression of the gene.