Repressor protein/gene, lambda

Figure 8.1 A region of DNA in the related bacteriophages lambda, 434, and P22 that controls the switch for synthesis of new phage particles. Two structural genes are involved in this switch one coding for a repressor protein and one coding for the Cro protein. Between these genes there is an operator region (OR) that contains three protein binding sites—ORl, OR2, and OR3.

Once the lambda repressor has been inactivated, the positive and negative control exerted by this repressor are abolished, and new transcriptional events can be initiated. The most important transcriptional event is that involved in the synthesis of another lambda protein called Cro. coded by a gene called cro. The gene cro is located almost adjacent to the gene cl which codes for lambda repressor. 

In the region separating these two genes are two kinds of sites, promoters and operators, to which each of the proteins of the switch can bind. When lambda repressor is bound to its operator, it covers... 

The leader sequence of the Serratia marcescens extracellular nuclease has been removed and the gene for the resulting nontransportable protein cloned behind the leftward promoter (PL) of lambda (Ahrenholtz, Lorenz Wackernagel, 1994). In the presence of a temperature-sensitive repressor (cl857), the cells can be induced to produce this altered enzyme by an increase in temperature. This produces the nuclease within the cell and, because it cannot be exported, its intracellular concentrations rise, rapidly degrading the cellular genome. Limitations to this system are that cell survival is reduced to only 2 x 10 5. 

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