PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Bacteriophage lambda”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,333 records · Page 74Linked to original sources
PubMed1970

Bacteriophage lambda; abortive infection of bacteria lysogenic for phage P2.

The efficiency of plating of wild-type lambda on a host lysogenic for P2 is less than 10(-6), and only a small number of infected cells produce progeny phage. Lambda can adsorb and inject its DNA normally in such cells; the DNA can circularize and is not nicked or degraded, but replication is severely impaired. Mutants of P2, which as prophages no longer interfere with lambda, have been isolated and found to be recessive to wild type, implying that P2 prophage codes for a diffusible product involved in lambda interference. The P2 gene product responsible for preventing lambda growth also kills recombination-deficient bacteria of the recB and recC classes under conditions where P2 does not normally kill the host. Mutants of lambda that are resistant to interference are recessive to wild-type lambda. Thus lambda actively participates in its own interference. The lambda-mutants that are resistant to interference are unable to synthesize at least two nonessential proteins. In addition, they are unable to grow on recombination-deficient bacteria of the recA class, but they can grow on recA recB double mutants.

Carbon Isotopes↗
PubMed1970

Mutation and recombination of bacteriophage lambda: effect of ultraviolet radiation.

Defects in the bacterial recB or recC or phage red or int gene did not impair ultraviolet light-induced clear mutations of lambda phage. Clear mutants of cI and cII genes were not enriched among RecA-promoted UV-induced recombinants between the N and O genes which closely encompass the c genes. No correlation was observed between UV-induced mutation and genetic recombination.

Coliphages↗
PubMed1971

Establishment and maintenance of repression by bacteriophage lambda: the role of the cI, cII, and c3 proteins.

To define the events necessary for the establishment and maintenance of repression in a lambda-infected cell, we have studied the requirements for efficient synthesis of the cI protein ("lambda-repressor"). Three classes of lambda mutants defective in the establishment of repression are also defective in the appearance of cI protein activity at the normal time. Two of these mutational classes (cII(-) and cIII(-)) probably result from inactivation of lambda-specified proteins, but the third class (cy(-)) may involve a structural defect. We conclude that at least three regulatory elements are likely to be required for the normal turn-on of cI protein synthesis in an infected nonlysogenic cell: cII and cIII proteins and an "active" y-region of lambda DNA. From these and other results, the complete role of cII and cIII proteins in the establishment of repression may involve a bifunctional regulatory activity: positive regulation of the cI gene and negative regulation of late genes. A possible molecular model for cII and cIII action is discussed. Since the cII and cIII genes are repressed by the cI protein under conditions of stable lysogeny, a separate mechanism is required for the maintenance of cI protein synthesis. After infection of a lysogen by cII(-) phage, the rate of increase of cI protein activity is substantially greater than after infection of a nonlysogen. From these and other results, the cI protein may also have a bifunctional regulatory activity: positive regulation of the cI gene and negative regulation of early lytic genes.

Autoradiography↗
PubMed1972

Precursor and product in bacteriophage lambda recombination.

Analyses of the time of recombination in bacteria infected with phage lambda and in spheroplasts infected with purified phage lambda DNA indicate a preponderance of recombination occurring before replication ("early recombination") after infection with tandem dimers formed in vitro compared to linear monomer DNA and phage infections. Among the early recombinants is a large fraction of cells that produces one recombinant type exclusively. Two suggestions are discussed-that a dimer-like molecule is the precursor of the recombinant progeny molecule and that one recombinant chromosome is the frequent or exclusive product of a recombinational event.

Centrifugation, Density Gradient↗
PubMed1972

An enhancing role for DNA synthesis in formation of bacteriophage lambda recombinants.

Recombination in some intervals of the map of phage lambda is associated with more DNA synthesis than in other intervals. Blockage of DNA synthesis by high temperature in a host temperature-sensitive for DNA synthesis results in the relative reduction of recombinant frequencies in those regions having the larger amounts of recombination-associated synthesis. Reduction of DNA synthesis at normal temperatures by a combination of the bacterial mutation and a mutation in one of the phage genes required for DNA synthesis has the same consequence. Therefore, DNA synthesis enhances recombinant particle formation more in some map intervals than in others.

Centrifugation, Density Gradient↗
PubMed1973

In vitro assembly of bacteriophage Lambda heads.

The assembly of plaque-forming particles in cell-free extracts of induced lambda lysogens was observed two ways. (i) DNA isolated from a lambda-related phage, 434 for example, is added to an extract of an induced lambda lysogen, and plaque-formers with the genotype of the added DNA are detected. (ii) One extract from an induced lambda lysogen that carries an amber mutation in one of the head genes (A, B, C, D, or E) is mixed with one carrying an amber mutation in a different head gene; an increase in the number of lambda plaque-formers is found over that in either extract alone. These plaque-forming particles have the properties of normal phage particles. They are resistant to DNase, although DNase added to an extract before addition of DNA prevents their appearance; they have a sensitivity to neutralizing antibody and a specificity of adsorption to bacteria characteristic of the source of the extract, but they have the genotype of the added DNA; and they have about the same bouyant density as phage particles. Mutants in genes B, C, or D can donate DNA to the phage formed by complementation between extracts of different mutants, but mutants in genes A or E cannot. Complementation occurs between a pair of extracts only if one (or both) is a DNA donor. This observation suggests a tentative pathway for head assembly: that the products of genes A and E act before those of B, C, and D.

Centrifugation, Density Gradient↗
PubMed1973

The 3'-terminal nucleotide sequences of bacteriophage lambda DNA.

Analyses of radioactive oligonucleotides in endonuclease digests of 3'-terminally labeled lambda DNA revealed the 3' terminal sequence -GTTACG for the l strand and -ACCCGCG for the r strand. These sequences, together with those previously known for the 5' cohesive ends, provide a total of 25 known base-pairs in the vicinity of the termini. When the cohesive ends are paired, the sequence between the nicks can be bisected by a 2-fold rotational axis of symmetry. Five of the first eight base-pairs, on either side of the axis, are rotationally symmetric. This symmetry may be involved in the recognition of the site by an enzyme responsible for formation of the cohesive ends.

Adenine Nucleotides↗