The last duplex base-pair of the phage lambda chromosome. Involvement in packaging, ejection and routing of lambda DNA.
cosN is the site at which the bacteriophage lambda DNA packaging enzyme, terminase, introduces staggered nicks to generate the cohesive ends of mature lambda chromosomes. Genetic and molecular studies show that cosN is recognized specifically by terminase and that effects of cosN mutations on lambda DNA packaging and cosN cleavage are well correlated. Mutations affecting a particular base-pair of cosN are unusual in being lethal in spite of causing only a moderate defect in cosN cleavage and DNA packaging. The particular base-pair is the rightmost duplex base-pair in mature chromosomes, at position 48,502 in the numbering system of Daniels et al; herein called position - 1. A G.C to T.A transversion mutation at position - 1, called cosN - 1T, reduces the particle yield of lambda fivefold, and the particles formed are not infectious. lambda cosN - 1T particles have wild-type morphology, and contain chromosomes that have normal cohesive ends. The chromosomes of lambda cosN - 1T particles, like the chromosomes of lambda + particles, are associated with the tail. lambda cosN - 1T particles, in spite of being normal structurally, are defective in injection of DNA into a host cell. Only approximately 25% of lambda cosN - 1T particles are able to eject DNA from the capsid in contrast to 100% for lambda +. Furthermore, for the 25% that do eject, there is a further injection defect because the ejected lambda cosN - 1T chromosomes fail to cyclize, in contrast to the efficient cyclization found for wild-type chromosomes following injection. The cosN - 1T mutation has no effect on Ca2+ mediated transformation by lambda DNA, indicating that the effect of the mutation on DNA fate is specific to the process of DNA injection. Models in which specific DNA : protein interactions necessary for DNA injection, and involving the rightmost base-pair of the lambda chromosome, are considered.
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Department of Microbiology, University of Iowa, Iowa City 52242.
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D010582:Bacteriophage lambda / Q000235:genetics* / Q000502:physiology / Q000648:ultrastructure; D001482:Base Composition; D001483:Base Sequence; D004279:DNA, Viral / Q000235:genetics* / Q000302:isolation & purification; D004926:Escherichia coli / Q000235:genetics*; D005814:Genes, Viral; D005816:Genetic Complementation Test; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D015345:Oligonucleotide Probes; D010957:Plasmids; D014161:Transduction, Genetic; D014170:Transformation, Genetic
D004279:DNA, Viral; D015345:Oligonucleotide Probes