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REGULATORY PATHWAYS - that the net effect of this proteins...

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REGULATORY PATHWAYS So far we have been considering simple regulatory systems with either a single repressor (Lac) or a single activator  (Mal). Often genes are regulated by a more complicated set of regulatory steps, which together can be thought of as a  r rr r . Although there are good methods that can be used to determine the order of steps in a regulatory pathway  (as will be discussed shortly), it is usually difficult at first to tell whether a given component identified by mutation  is acting directly on the DNA of the regulated gene or whether it is acting at a step upstream in a regulatory  pathway. For example, it will often be the case that a recessive trans-acting mutation that causes constitutive  expression is not an actual repressor protein, but a protein acting upstream in a regulatory pathway in such a way 
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Unformatted text preview: that the net effect of this proteins is to cause repression of gene function. The best way to represent this situation is to call the gene product a n nn n and to reserve the term repressor for cases in which we know that the protein actually shuts off transcription directly by binding to an operator site. Similarly, the best way to represent a gene defined by a recessive, trans-acting mutation that causes uninducible expression as a p pp p until more specific information can be obtained about whether or not the gene product directly activates transcription. The diagrams to be used are shown below....
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