Deoxyribonucleic acid, bacteriophage (Lambda Phage) from Escherichia coli

Non-methylated lambda DNA is completely digested by Bcl I, Cla I, Mbo I, Mbo II, Taq I or Xba I whereas methylated lambda DNA is only partially cleaved.

The lambda phage has an icosahedral head and a long tail terminating in a single fiber. At both ends of the 5′ termini are complementary 12-nucleotide single strand sequences that contribute to the cohesive ends (cos region) of the DNA. The tail of the phage latches on the host outer membrane receptor and injects phage DNA into the cell. The phage converts the E. coli to a lysogenic state in which the phage functions are repressed and the phage genome may remain dormant (prophage) for a long time. This property is seen in bacteriophages that carry CII and CIII genes that are responsible for CI expression. Bacteriophages with CI mutation in the CI gene are able to maintain a lysogenic state at defined temperatures.
Infecting E. coli strain GM119 with lambda C1857 strain creates E. coli lysogen cultures. The phage is released from E. coli cell pellets by lysing with a high salt buffer, pH 8.0. The crude mixture is passed through a series of enzymatic steps, multiple cesium gradients, and phage DNA is dialyzed against 1mM Tris-HCl, pH 8.0, and 1 mM magnesium chloride. The DNA is finally extracted by phenol-chloroform solution.