Dimers phage

EMPl, selected by phage display from random peptide libraries, demonstrates that a dimer of a 20-residue peptide can mimic the function of a monomeric 166-residue protein. In contrast to the minimized Z domain, this selected peptide shares neither the sequence nor the structure of the natural hormone. Thus, there can be a number of ways to solve a molecular recognition problem, and combinatorial methods such as phage display allow us to sort through a multitude of structural scaffolds to discover novel solutions. 

The pJuFo system also has the potential to display homodimers or homomultimeric proteins on the surface of the phage. This is possible because the protein of interest is expressed independent of the phage proteins. Therefore, the Fos-ORF fusion protein is secreted to the periplasm, the Fos portion interacts with Jun to attach the protein to the phage, and other copies of the Fos-ORF protein can interact with each other to form a dimer or multimer. However, the successful display of homodimers has not been demonstrated in practice. 

Figure 5.16 Illustration of the manner by which the virion of a filamentous single-stranded phage (such as M13 or fd) leaves an infected cell without lysis. The A protein passes first through the membrane at a site on the membrane where coat protein molecules have first become imbedded. The intracellular circular DNA is coated with dimers of another protein, gp5, which is displaced by coat protein as the DNA passes through the intact membrane.

The correlation between definite photoproducts and biological action of ultraviolet light discussed in this section is confined to a particular action of ultraviolet light, namely an inactivating or lethal action. Microorganisms are killed, DNA synthesis in cells is inhibited, transforming DNA is inactivated, template activity of DNA is reduced, and phage and viruses are inactivated because the pyrimidine dimer which is formed in-strand is apparently able to provide a block which hinders DNA or RNA replication. 

The isolation of an antibody is an extremely useful first step toward understanding the function of the protein to which it binds. scFvs derived from phage antibody libraries have been used in immunofluorescence, immunoprecipitation, fluorescence-activated cell sorting, Western blotting, and inhibition of function studies, both in vivo, in tissue culture cells, and in vitro. In this sense, they can essentially be used in the same way as conventional hybridoma-derived antibodies. They have the advantage, however, that the genes for the variable regions are cloned simultaneously with selection. This allows the fusion of functional elements, such as dimerization domains, effector or detector functions to selected scFvs [38], the re-creation of complete... 

Wickner and colleagues have demonstrated a role for the E. coli dnaK protein in replication of bacteriophage PI (Wickner, 1990). In PI replication, the phage repA protein binds specifically to the PI origin of replication it appears to be a monomeric repA that binds to the origin with high affinity. Dimers of repA, in a 2 2 subunit complex with the E. coli... 

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