Genetic engineering types

Restriction enzymes can be classified into three types, type 1, 11, or 111, based on their enzymol-ogy and cofactor requirements (Wilson, 1988). Because types I and 111 cut DNA variably or with low efficiency, they are not typically used for genetic engineering. Type II enzymes can reproducibly and efficiently cleave specific nucleotide sequences ( restriction sites ), making them the most reliable set of restriction enzymes for DNA manipulation. 

Biological processes are also being studied to investigate abiHty to remove sulfur species in order to remove potential contributors to acid rain (see Air pollution). These species include benzothiophene-type materials, which are the most difficult to remove chemically, as weU as pyritic material. The pyrite may be treated to enhance the abiHty of flotation processes to separate the mineral from the combustible parts of the coal. Genetic engineering (qv) techniques are being appHed to develop more effective species. 

In 1989, two enzymes based on genetic engineering techniques were introduced, ie, a cloned alkaline protease (IBIS) and a protein engineered Subtihsin Novo (Genencor, California). Lipase and ceUulase types of detergent enzymes have also begun to appear. 

Soluble receptor constructs Etanercept This genetically engineered drug consists of the extracellular-part of the TNF-receptor type I and the Fc portion of human IgG. Its application in rheumatoid arthritis mirrors that of infliximab. 

The case of canola is extraordinary because of the very high level accumulations (50-fold) of leaf-type carotenoids in seeds when the gene was introduced under the seed-specific promoter, napin. The exalbuminous seeds of canola differ from those of genetically engineered rice cereal grains in that they have chloroplasts, which may explain the capacity for hyperaccumulation of carotenoids. 

Apart from mode of action and kinetics of wild type enzymes structure function relationships of these industrially important enzymes is of high interest to provide the necessary knowledge for genetic engineering of desired properties. As a first approach the identification of catalytically important residues was addressed in conjunction with the elucidation of the three dimensional structure [15]. 

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