Nexus - 0601 - New Times Magazine-pages

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that occur are influenced by enzymes, which are also proteins. moters from one coding sequence can be removed and placed in Thus, scientists who study development spend a lot of effort front of another coding sequence to change when or where the describing protein patterns. protein is made. For example, when the promoter for casein, the By studying which proteins are present in different tissues and major protein in milk, is removed and put in front of the coding organs, biologists have learned that each cell has several thousand sequence for human growth hormone, it causes human growth different proteins, but most of the proteins are very rare in the hormone to be made in cow's milk, instead of casein. Of course, cell. A few hundred proteins may be moderately abundant, and a in order to make human growth hormone in cow's milk, the engi- few may be quite abundant. Also, some proteins are found in all neered gene has to be incorporated into the genetic material of the inds of cells and at all times in development, whereas other pro- cow. There are many ways to do this, but I will not go into the teins are only present in a particular tissue or at a specific time. details here. For example, the gluten proteins responsible for the elasticity of The general process of moving genes between species is called read dough are found only in the seed, and they are present there ‘transformation’, and the result is a 'transgenic' organism. Lately, in very large amounts. In contrast, the enzyme that splits glucose transgenic organisms are being called ‘genetically modified organ- as a first step in releasing energy is found in all living cells, but in isms’ (GMOs). fairly small amounts. Some proteins are made in response to Details of the Terminator Technology environmental changes, such as increases in The key to Terminator is the ability to present during the life of a particular plant. fo confine that toin to seeds. To accomplish tol how much of which kinds of proteins plan sto take the promoter fom a sene nor we presen toconrolvmchzens | The Terminator | lactated sin ced deyclopnent in and the oder of aminoacids and the tenath | DALENE OffeFS AM | erase goin throush the last stages of of the chain are unique for each kind of pro- ingenious method development. tein. Each unique amino acid sequence is In the Terminator patent, the authors use a specified by a code on a chromosome in the for keeping the promoter from a cotton LEA (late embryoge- cell's nucleus. The code is made of DNA. . nesis abundant) gene. This gene is one of the _ For the urposes of this discussion, a gene toxin gene from last to be activated. ts protein is not made is a piece o that contains the . . . until the seed is full-sized, has accumu- code for a specific protein. Genes are being active until lated most of its storage oil and protein, present in specific places along the and is drying down in preparation for length of the chromosomes. long after the the dormant period in between leaving It turns out that just about every cell the parent plant and germinating in the has two full sets of genes (one set of farmers plant soil. If the engineered gene has the chromosomes from the sperm, and one their crops same pattern of expression, LEA-pro- from the egg) which code for the pro- . moter-directed proteins should be made teins made in all of the tissues and in high quantities, only in seeds, and organs that an individual plant will late in development. need during its life cycle. However, It is important for the cotton seeds to only those genes whose proteins are go through most of their growth before needed in a particular cell will be used the toxin acts, because the cotton fibre by that cell. These are the active is an outgrowth of the seed coat and is genes. The other genes just sit there on made as the cotton develops. Further, the chromosomes, inactive in that cell, after the cotton fibres are removed (for but active somewhere else in the plant. human use), the seed is then crushed for oil and protein, both of Whether a gene is active or not depends on complex interac- which are eaten by people and livestock. The cotton crop would tions between the DNA and other molecules in the cell. be of little use to a farmer if the seeds did not mature normally Specifically, a typical gene can be divided into parts. The first before dying. part is a stretch of DNA responsible for interacting with the cell or As for a toxin, there are several possibilities discussed in the the environment, and is called the 'promoter'. The second part patent, but the patent authors recommend a ribosome inhibitor actually contains the code for the order of amino acids in the pro- protein (RIP) from the plant Saponaria officinalis. This protein tein, and is called the 'coding sequence’. When the gene is active, works in small quantities to stop the synthesis of all proteins. the promoter is interacting with other molecules in a way that Since cells need proteins for almost everything, they die fairly allows the coding sequence to direct the synthesis of a specific quickly when they can't make proteins. According to the patent, protein (through a complex set of steps). the RIP is non-toxic to organisms other than plants. Genetic engineering can be defined as the process of manipulat- The manipulations of DNA required to engineer a seed-specific ing the pattern of proteins in an organism by altering genes. promoter/toxin coding sequence gene are done in test-tubes and Either new genes are added or existing genes are changed so that _ bacteria, and then the altered gene is put into a cotton plant, using they are made at different times or in different amounts. one of several possible well-established methods. Because the genetic code is similar in all species, genes taken However, this is not all there is to it. If this were all, then as from a mouse can function in a corn plant, and so on. Also, pro- soon as the transgenic plant went through its life cycle and came moters from one coding sequence can be removed and placed in front of another coding sequence to change when or where the protein is made. For example, when the promoter for casein, the major protein in milk, is removed and put in front of the coding sequence for human growth hormone, it causes human growth hormone to be made in cow's milk, instead of casein. Of course, in order to make human growth hormone in cow's milk, the engi- neered gene has to be incorporated into the genetic material of the cow. There are many ways to do this, but I will not go into the details here. The general process of moving genes between species is called ‘transformation’, and the result is a 'transgenic' organism. Lately, transgenic organisms are being called ‘genetically modified organ- isms' (GMOs). patent offers an ingenious method for keeping the toxin gene from being active until long after the farmers plant their crops. NEXUS - 27 The Terminator DECEMBER 1998 - JANUARY 1999