臺灣博碩士論文加值系統

異染色質結（heterochromatic knobs）是玉米細胞分裂前期（prophase）染色體上比較膨大、染色深的地方。其對於玉米遺傳上的影響主要是（1）具有新中節活性（neocentromere activity）以及（2）造成染色質丟失（chromatin elimination）。前人由玉米基因組中分離出兩種銜接排列的重複性序列（tandemly repeated sequences），180-bp序列及TR-1序列（350-bp），皆聚集在異染色質結。這兩種重複性序列中有兩段（分別為12 bp及31 bp）相似度在60﹪以上。而且發現180-bp與B染色體中節序列中的90 bp有72﹪的相似度，因此推測180-bp重複性序列可能與異染色質結具新中節活性有關。由於180-bp序列已經在玉米以及其近緣種中被詳細研究過，而有關TR-1的資料卻很少。因此本研究從不同的玉米品系及其近緣種分離出TR-1重複性序列，分析其分子結構。發現TR-1是由A、B/B’及C序列所組成的複合體，並且是以180 bp而不是350 bp為重複單位。B/B’與180-bp重複性序列有相似性的片段，推測B/B’的來源是180-bp序列。A、C序列由於：（1）兩者有高相似度的片段；（2）C序列的後面都接著A序列；（3）兩者A＋T的含量都大約是70﹪；所以將C＋A視為另一種180 bp的重複性序列。A、B/B’及C序列與B染色體中節序列也有許多相似性的片段，所以TR-1複合體在新中結活性上扮演重要的角色。另外，論文中也討論了TR-1複合體形成的可能機制。

Heterochromatic knobs are enlarged and deeply stained regions in prophase chromosomes of maize. The main genetic effects of knobs are (1) neocentromere activity and (2) chromatin elimination. Two classes of tandemly repeated sequences associated with knobs have been isolated from the maize genome, the 180-bp repeat and TR-1 element (350-bp). Two segments (12 bp and 31 bp) in these repeats show homology of more than 60%, and the 180-bp repeat has a 72% similarity to a 90-bp stretch of the maize B chromosome centromere sequence. It has been suggested that the 180-bp repeat may be responsible for neocentromere activity. The 180-bp repeat has been extensively studied in maize and its relatives, but the molecular structure of the TR-1 element is not clear. In this study, we isolated TR-1 elements from various lines of maize and its relatives and analysed their structures. Our results demonstrates that TR-1 element is composed of A, B/B’, C repeats, and the unit length is 180 bp but not 350 bp as previously reported. There are some homology between segments of B/B’ and the 180-bp repeat, so we presume that 180-bp repeat is the ancestor of B/B’. The following reasons suggest that C+A may be actually a class of repetitive sequence with a unit length of 180 bp: (1) A and C show high homology in nucleotide sequences; (2) C is always before A in the clones analysed; (3) A and C have the same percentage (approximately 70%) of A+T. The role of TR-1 in neocentromere activity and the mechanism of the formation of TR-1 are discussed.

中文摘要.……..………………………………………………………...i
英文摘要..……………………………………………………………...ii
壹、前言…………………………………………………………….….1
貳、材料與方法………………………………………………………..5
一、植物材料……….…………………………………………….5
二、植物總DNA的抽取……….………………………………..5
三、質體DNA的抽取…………….……………………………..7
四、TR-1重複性序列的選殖與定序..….……………………….8
五、南方氏雜交……………………..….……………………….11
參、結果……………………………………………………………….13
一、TR-1是由A、B、C三種序列組成的複合體..…………..13
二、A序列的分析……………………………………………….13
三、B序列的分析……………………………………………….18
四、C序列的分析……………………………………………….25
五、A、B、C三序列與其他序列的比對………………………25
六、基因組南方氏雜交………………………………………….32
肆、討論……………………………………………………………….35
一、TR-1是由不同重複性序列組成的複合體………………...35
二、TR-1在玉米演化過程中出現的時序………………………35
三、TR-1是如何形成的…………………………………………36
四、異染色質結中重複性序列與新中結活性的關係………….39
五、異染色質結形成的原因…………………………………….41
伍、參考文獻………………………………………………………….42
附錄1、各選殖體A1序列之對齊排列……………………………...47
附錄2、各選殖體A2序列之對齊排列………………………………48
附錄3、各選殖體B序列之對齊排列……………………………….49
附錄4、各選殖體2/3 B序列之對齊排列……………………………53
附錄5、各選殖體C序列之對齊排列……………………………….55

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