Phage mutant

Escherichia coli (strain 201 infected with bacteriophage T4amBL292, a maturation defective phage mutant, host-coded activity which is a component of T4 dNTP-synthesizing enzyme complex [2]) [2]... 

The T4 DNA ligase has been purified from E. coli B cells infected with the wild-type T4 phage (4) or the replication-defective phage mutant awN82 (32). Ligase activity can be detected 5 min after infection and reachps a maximum at 20 min (33). A purified enzyme is obtained after a 1000-fold purification. 

Rottlander, E., Trautner, T. A. Genetic and transfection studies with B. subtilis phage SP50. I. Phage mutants with restricted growth on B. subtilis strain I68. Molec. gen. Genet. 108, 47-60 (1970). 

Fig. 5. Generation of mutants using single-stranded DNA. After cloning the target gene into M13, the phage is propagated in the E. coll dut, ung strain of E.

Protein engineering is now routinely used to modify protein molecules either via site-directed mutagenesis or by combinatorial methods. Factors that are Important for the stability of proteins have been studied, such as stabilization of a helices and reducing the number of conformations in the unfolded state. Combinatorial methods produce a large number of random mutants from which those with the desired properties are selected in vitro using phage display. Specific enzyme inhibitors, increased enzymatic activity and agonists of receptor molecules are examples of successful use of this method. 

FIG. 1 Monolayer of T7 phage heads. Cryoelectron micrograph of tailless mutant of T7 bacteriophage. Bar 50 nm. (From Ref. 42. Copyright 1997 Cell Press.)... 

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. 

Exit of the virus from the cell occurs as a result of cell lysis. The phage codes for a lytic enzyme, the T4 lysozyme, which causes an attack on the peptidoglycan of the host cell. The burst size of the virus (the average number of phage particies per cell) depends upon how rapidly lysis occurs. If lysis occurs early, then a smaller burst size occurs, whereas slower lysis leads to a higher burst size. The wild type phage exhibits the phenomenon of lysis inhibition, and therefore has a large burst size, but rapid lysis mutants, in which lysis occurs early, show smaller burst sizes. 

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... 

The observations that mutation frequencies are elevated severalfold above normal levels in mutants which constitutively express their SOS-functions (32) and that the mutation frequency of unirradiated phage is elevated by growing them on irradiated (i.e. SOS-induced) bacteria (33), have been invoked to argue for the notion that mutagenesis via SOS-processing may be indirect. 

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