We have derived bias-corrected X-ray luminosity functions (XLFs) of sources detected in a uniformly selected sample of 14 E and S0 galaxies observed with Chandra ACIS-S3. The entire sample yields 985 pointlike X-ray sources, with typical detections of 30–140 sources per galaxy. After correcting for incompleteness, the individual XLFs are statistically consistent with a single power law of a (di...

Nonhomologous DNA end-joining (NHEJ) is a major pathway of DNA double-strand break (DSB) repair in mammalian cells, and it functions to join both specifically programmed DSBs that occur in the context of V(D)J recombination during early lymphocyte development as well as general DSBs that occur in all cells. Thus, defects in NHEJ impair V(D)J recombination and lead to general genomic instability...

Nonhomologous end joining repairs DNA double-strand breaks created by ionizing radiation and V(D)J recombination. Ku, XRCC4/Ligase IV (XL) and XLF have a remarkable mismatched end (MEnd) ligase activity, particularly for ends with mismatched 3' overhangs, but the mechanism has remained obscure. Here, we showed XL required Ku to bind DNA, while XLF required both Ku and XL to bind DNA. We detecte...

The Ku-binding motif (KBM) is a short peptide module first identified in APLF that we now show is also present in Werner syndrome protein (WRN) and in Modulator of retrovirus infection homologue (MRI). We also identify a related but functionally distinct motif in XLF, WRN, MRI and PAXX, which we denote the XLF-like motif. We show that WRN possesses two KBMs; one at the N terminus next to the ex...

We present the first X-ray Luminosity Function (XLF) for an optically-selected sample of 49 nearby poor clusters of galaxies and a sample of 67 Abell clusters with z ≤ 0.15. We have extended the measured cluster XLF by more than a factor of 10 in X-ray luminosity. Our poor cluster sample was drawn from an optical catalog of groups with 0.01 ≤ z ≤ 0.03 composed of Zwicky galaxies. The X-ray emis...

Non-Homologous End Joining (NHEJ) is one of the two major pathways of DNA Double Strand Breaks (DSBs) repair. Mutations in human NHEJ genes can lead to immunodeficiency due to its role in V(D)J recombination in the immune system. In addition, most patients carrying mutations in NHEJ genes display developmental anomalies which are likely the result of a general defect in repair of endogenously i...

Inositol hexakisphosphate (InsP6) is a member of the inositol polyphosphate group that participates in numerous intracellular signaling pathways. Cheung and colleagues previously reported that InsP6 stimulated double-strand break repair by nonhomologous end joining (NHEJ) in cell-free extracts and that InsP6 binding by the Ku70/80 subunit of the DNA-dependent protein kinase (DNA-PK) was require...

We present theoretical models for populations of low-mass X-ray binaries in two elliptical galaxies: NGC3379 and NGC4278. The models are calculated with the recently updated StarTrack code (Belczynski et al. 2007), and are targeted to modeling and understanding the origin of the X-ray luminosity functions (XLF) in these galaxies. For the first time we explore the population XLF down to luminosi...

Non-homologous end-joining is a major pathway of DNA double-strand break repair in mammalian cells, deficiency in which confers radiosensitivity and immune deficiency at the whole organism level. A core protein complex comprising the Ku70/80 heterodimer together with a complex between DNA ligase IV and XRCC4 is conserved throughout eukaryotes and assembles at double-strand breaks to mediate lig...

A complex of two related mammalian proteins, SFPQ and NONO, promotes DNA double-strand break repair via the canonical nonhomologous end joining (c-NHEJ) pathway. However, its mechanism of action is not fully understood. Here we describe an improved SFPQ•NONO-dependent in vitro end joining assay. We use this system to demonstrate that the SFPQ•NONO complex substitutes in vitro for the core c-NHE...