Abstract
金屬硫蛋白（metallothionein，MT）是一低分子量且富含半胱胺酸的蛋 白質。其普遍存在於各種生物體內，且可能與重金屬的解毒、代謝及暫時 的貯存有關。目前已知大多數禽類只存在一種MT。先前分析兩種不同屬的 鴨類，番鴨和菜鴨肝臟內之MT胺基酸序列，發現和雞者完全一樣。為了探 討這些禽類MT在基因上的變化，我們自番鴨和菜鴨的 cDNA library中選 殖出MTcDNA，其轉譯區與雞的MTcDNA甚為相似，有差異的鹽基只位於搖擺 位（wobble position）上，並不影響所對應胺基酸的不同。隨後我們嘗 試選殖genomic DNA中的MT基因。首先以聚合酵素連鎖反應（PCR）的方法 先擴增genomic DNA中的MT基因，對該產物做選殖及定序發現它包含三個 exons及兩個introns。利用PCR產物來選殖番鴨和菜鴨基因庫可得到數個 陽性選殖株（positive clones），然而在次選殖的過程並不順利。此外 ，我們也利用番鴨和菜鴨雜交所得的子代：土番鴨及鴃鶗鴨，來探討不同 的親代對其子代的MT基因表現的影響，利用反轉錄酵素-聚合酵素連鎖反 應（RT-PCR）及cDNA序列的分析得知，在經鎘誘導後的雜種鴨體內的 MT mRNA之MT在雜交後代都能表現出來。 Methionein (MT) is a low-mocecular-weight, cysteine-rich protein which commonly exists in various organisms. It has been suggested that MT may play an important role in detoxification of heavy metals and metabolism or transient storage of the essen tial metals. It was shown that only one kind of MT exists in most of avian. Previously, the protein sequences of MTs from two genera of ducks, Moscovy and Tasi duck, were determined and they were found to be identical to chicken MT. In order to investi- gate the variation among those avian MT genes, we constructed c- DNA libraries and isolated MT cDNA for both ducks. The coding region of both cDNAs were similar to that of chicken MT except few differences at wobble poitions. We further tried to clone the genomic DNA for both ducks. At first, polymerase chain re- action ( PCR ) was used to amplify MT gene from genomic DNA of both ducks. The PCR product was cloned and sequenced and the gene structure was compared with that of other avian species. The PCR productwas also used as a probe to screen MT gene from a constructed genomic library. Several positive clones were ob- tained. However, the subcloning is not successful. Expression of MT gene in the hybrids of Mascovy and Tasi ducks,i.e.,Mule duck and Hinney duck, were also investigated. Reverse transcriptase - PCR ( RT - PCR ) was used to estimated MT mRNA production after cadmium induction. It was found that both of parents MT gene could be expressed after the hybrids were treated with cadmium.