Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/81472
標題: Restriction Enzymes
限制酶
作者: K. Y. Lee
李國鏞
B. Y. Chang
張邦彥
關鍵字: methylase;修飾酶;Restriction Enzymes;限制酶
Project: Horticulture NCHU, Volume 11, Page(s) 49-57.
興大園藝, Volume 11, Page(s) 49-57.
摘要: 
限制酶可分為第一限制酶,第二限制酶以及第三限制酶等三種。其實第一類限制酶的分子量為450,000-750,000之關係由三個次單位組而成。次單位之ㄧ為hsd R基因的產物,專司外來之DNA的剪切。hsd M 基因的產物專司自身或者外來DNA的修飾,而 hsd S 基因產物則掌理DNA的識別。該酶的分布,據目前學界的研究,僅侷信於腸細菌科的微生物。其在菌體的功用在於防禦他DNA的入侵。
與第一類限制沒有同一防禦做用的另一酶,為第三限制酶。此酶的分子量約為200,000,由兩個次單位組合而成。,其一從事外來DNA的剪切,而另一從事DNA的修飾及識別含有此酶的體系。計有P1筮菌體,P5質體等。
第三限制酶的結構,較上述兩類限制酶,均為簡單及細小。此分子量約僅為上述酶類的十分之ㄧ。在此,限制酶的活性與修飾媒活性個分屬兩個獨立的蛋白質,各其自皆能識別標的DNA。這種限制酶分布甚廣,可自數百種菌體中覓得,但其真正的功能則不得而知。由於其具有極專一及精確的剪切能力,目前已經成為遺傳工程的利器。

Three types of restriction enzymes are recognized today. They are Type Ⅰ, Type Ⅱ and Type Ⅲ enzymes. Each of the Type Ⅰ enzyme, with a molecular weight around 451,000-750,000, is composed of three subunits, the latter are encoded by three separats genes. The product of hsd R gene is responsible for foreign DNA restriction. The product of hsd M gene engages in DNA methylation, and the procuct of hsd S gene specializes in DNA recognition. The Type Ⅰ enzymes, to date, are found only in Entero-bacteriaceae, they are key components of the cell defense mechanism.
Like Type Ⅰ enzymes, the Type Ⅲ restriction enzymes are also involved in defense systems. The individual enzyme, with a molecular weight about 200,000, consists of two subunits. One of the two has the restroction activity and another the duall functions of methylation and recognition. The enzymes so far studied are integral parts of the phage P1 and plosmid P15 resistance arsenal.
In comparison with the enzymes mentioned above, Type Ⅱ restriction enzymes are comsiderably less complex and quite a bit smaller. They are close to one tenth the size of their larger relatives in terms of molecular weight. The restriction activity and methylation activisity are separate proteins, each of which is capable of recognizing the target DNA. The enzymes are widespread, they have been found in hundreds of microbes. Their real function in cell is far from being clear. However, their highly specific DNA cleavage ability has made them the indispenable tools of genetic engineering.
URI: http://hdl.handle.net/11455/81472
ISSN: 0255-5921
Appears in Collections:園藝學系
第11期

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