Phage functional

Mandel, M., Berg, A. Cohesive sites and helper phage function of P2, lambda, and 186 DNAs. Proc. nat. Acad. Sci. (Wash.) 60, 265-268 (1968). 

Yi, H., Ghosh, D., Ham, M.H., Qi, J., Barone, P.W., Strano, M.S., Belcher, A.M., 2012. M13 phage-functionalized single-waUed carbon nanotubes as nanoprobes for second near-infrared window fluorescence imaging of targeted tumors. Nano Lett. 12, 1176-1183. 

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. 

Structural scaffolds can be reduced in size while function is retained Phage display of random peptide librciries... 

Crameri, R., and Suter, M. (1993). Display of biologically active proteins on the surface of filamentous phages a cDNA cloning system for selection of functional gene products linked to the genetic information responsible for their production. Gene 137, 69-75. 

Sche, P. P., McKenzie, K. M., White, J. D., and Austin, D. J. (1999). Display cloning functional identification of natural product receptors using cDNA-phage display. Chem. Biol. 6, 707-716. 

In general, virus receptors carry out normal functions in the cell. For example, in bacteria some phage receptors are pili or flagella, others are cell-envelope components, and others are transport binding proteins. The receptor for influenza vims is a glycoprotein found on red blood cells and on cells of the mucous membrane of susceptible animals, whereas the receptor site of poliovirus is a lipoprotein. However, many animal and plant viruses do not have specific attachment sites at all and the vims enters passively as a result of phagocytosis or some other endocytotic process. 

Temperature-sensitive mutations are those which allow a virus to replicate at one temperature and not at another, due to a mutational alteration in a virus protein that renders the protein unstable at moderately high temperatures. For instance, temperature-sensitive mutants are known in which the phage will not be replicated in the host at 43 °C but will at 25 °C, although the host functions at both temperatures. Such mutations are called conditionally lethal, since the virus is unable to reproduce at the higher temperature, but replicates at the lower temperature. 

Figure 5.17 Genetic map of phage T 7, showing gene numbers, approximate sizes, and functions of the gene products.

Lytic growth of Mu can occur either upon initial infection, if the c gene repressor is not formed, or by induction of a lysogen. In either case, replication of Mu DNA involves repeated transposition of Mu to multiple sites on the host genome. Initially, transcription of only the early genes of Mu occurs, but after gene C protein, a positive activator of late RNA synthesis, is expressed, the synthesis of the Mu head and tail proteins occurs. Eventually, expression of the lytic function occurs and mature phage particles are released. 

Because Mu integrates at a wide variety of host sites, it can be used to induce mutants at many locations. Also, Mu can be used to carry into the cell genes that have been derived from other host cells, a form of in vivo genetic engineering. In addition, modified Mu phage have been made artificially in which some of the harmful functions... 

Mainly the outer membrane ferrichrome receptor and transporter FhuA will be discussed because most structural and functional studies have been performed with this protein. In fact, FhuA was the first outer membrane protein identified (called TonA), with known functions as a phage and colicin receptor, that are related to iron transport (for a historical account, see Braun and Hantke 1977). 

---