Molecular and biochemical characterization of new X-ray-sensitive hamster cell mutants defective in Ku80.

Ku, a heterodimer of approximately 70 and approximately 80 kDa subunits, is a nuclear protein that binds to double-stranded DNA ends and is a component of the DNA-dependent protein kinase (DNA-PK). Cell lines defective in Ku80 belong to group XRCC5 of ionizing radiation-sensitive mutants. Five new independent Chinese hamster cell mutants, XR-V10B, XR-V11B, XR-V12B, XR-V13B and XR-V16B, that belong to this group were isolated.

Expression of DNA-dependent protein kinase holoenzyme upon induction of lymphocyte differentiation and V(D)J recombination.

Murine preB lymphocytes grow in tissue culture in the presence of stromal cells and interleukin 7 (IL-7), and can be induced to differentiate to surface-immunoglobulin-positive B cells in vitro by withdrawal of IL-7. Upon differentiation, proliferation ceases, and upregulation of Rag-1 and Rag-2 expression, and induction of V(D)J immunoglobulin-gene rearrangements occur. DNA-dependent protein kinase (DNA-PK) is required for effective V(D)J recombination and repair of DNA double-strand breaks.

Lack of detectable defect in DNA double-strand break repair and DNA-dependent protein kinase activity in radiosensitive human severe combined immunodeficiency fibroblasts.

The initial step of the V(D)J recombination occurs through the generation of a DNA double-strand break (dsb). Defects in the DNA-dependent protein kinase complex (DNA-PK) result in an inability to perform either V(D)J recombination or any dsb repair effectively. The human autosomal T-B-severe combined immunodeficiency (SCID) condition is characterized by an absence of both B and T lymphocytes and is accompanied in some patients by an increase in gamma-ray sensitivity (T-B-RS SCID) comparable to that found in mouse SCID cells.

DNA-dependent protein kinase defects are linked to deficiencies in DNA repair and V(D)J recombination.

DNA-dependent protein kinase is a nuclear serine/threonine kinase whose catalytic properties are expressed only when the enzyme is bound to DNA ends or other discontinuities in the DNA. DNA-PK comprises two components: one mediates binding to DNA and corresponds to the heterodimeric human autoimmune antigen Ku; the other, DNA-PK catalytic subunit (DNA-PKcs), is a polypeptide of approximately 450 kDa. DNA-PK deficiencies are associated with certain mutant rodent cell lines that display defects in DNA double strand break repair and V(D)J recombination.

Defective DNA-dependent protein kinase activity is linked to V(D)J recombination and DNA repair defects associated with the murine scid mutation.

Murine cells homozygous for the severe combined immune deficiency mutation (scid) and V3 mutant hamster cells fall into the same complementation group and show similar defects in V(D)J recombination and DNA double-stranded break repair. Here we show that both cell types lack DNA-dependent protein kinase (DNA-PK) activity owing to defects in DNA-PKcs, the catalytic subunit of this enzyme. Furthermore, we demonstrate that yeast artificial chromosomes containing the DNA-PKcs gene complement both the DNA repair and recombination deficiencies of V3 cells, and we conclude that DNA-PKcs is encoded by the XRCC7 gene.

DNA-dependent protein kinase activity is absent in xrs-6 cells: implications for site-specific recombination and DNA double-strand break repair.

DNA-dependent protein kinase (DNA-PK) is a nuclear serine/threonine protein kinase composed of a catalytic subunit called p350 and a DNA binding component termed Ku. Ku consists of two tightly associated polypeptides of approximately 70 kDa and 80 kDa (Ku80). An intriguing feature of DNA-PK is that it binds to DNA ends and other discontinuities in DNA and requires these structures for its activation.

Bacillus anthracis but not always anthrax.

Gram-positive bacilli isolated during epidemiological investigations which, on the basis of conventional tests, resemble Bacillus anthracis but which fail to produce the capsule or to induce anthrax in test animals have long been dismissed in clinical and veterinary laboratories as B. cereus or simply as unidentified Bacillus spp. and thereupon discarded as inconsequential.

The Charing Cross Hospital Child Development Centre: a description of its work ad an evaluation of its first 385 patients.

Charing Cross Hospital provides facilities for the study of handicapped children in a normal nursery which forms part of its Child Development Centre. The period of assessment varies from one day to three weeks; the advantages of prolonged assessment are discussed. Parental involvement and support, and the teaching of medical students are emphasized.