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Lambda Adsorption to Cells
Phage particles ought not to inject their DNA wantonly into anything. For the highest survival value, they should release their encapsidated DNA only after they have made stable contact with a suitable host cell. Not unexpectedly, then, lambdoid phage make specific contacts with structures on the outer surface of E. coli. Only when the proper receptor is present can the phage adsorb and inject.
Many different membrane structures are used by different phage in the adsorption and injection process. The laboratory form of lambda that has been studied for the last two decades uses a protein specified by the maltose operon. It is named the LamB protein because its first known function was lambda adsorption and only later was it discovered to be part of the maltose operon. The normal cellular function of the LamB protein is to create a pore through the outer membrane somewhat larger than the pores usually found there. This maltose-inducible pore is necessary for the diffusion of maltodextrins, to the periplasmic space. The pore is also necessary if maltose is present at low concentrations. Induction of the maltose operon increases the levels of this protein and speeds the adsorption process; eliminating synthesis of this protein or mutationally altering it makes cells resistant to lambda and can leave them Mal-.
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