Original Paper

Cell Death and Differentiation (2015) 22, 890–897; doi:10.1038/cdd.2015.22; published online 13 March 2015

XLS (c9orf142) is a new component of mammalian DNA double-stranded break repair

A Craxton1, J Somers1, D Munnur1, R Jukes-Jones1, K Cain1 and M Malewicz1

1MRC Toxicology Unit, Hodgkin Building, Lancaster Road, Leicester LE1 9HN, UK

Correspondence: M Malewicz, MRC Toxicology Unit, Hodgkin Building, Lancaster Road, Leicester LE1 9HN, UK. Tel: +44 116 252 5579; Fax: +44 116 252 5616; E-mail: mm531@le.ac.uk

Received 24 January 2015; Accepted 9 February 2015
Advance online publication 13 March 2015

Edited by G Melino



Repair of double-stranded DNA breaks (DSBs) in mammalian cells primarily occurs by the non-homologous end-joining (NHEJ) pathway, which requires seven core proteins (Ku70/Ku86, DNA-PKcs (DNA-dependent protein kinase catalytic subunit), Artemis, XRCC4-like factor (XLF), XRCC4 and DNA ligase IV). Here we show using combined affinity purification and mass spectrometry that DNA-PKcs co-purifies with all known core NHEJ factors. Furthermore, we have identified a novel evolutionary conserved protein associated with DNA-PKcs—c9orf142. Computer-based modelling of c9orf142 predicted a structure very similar to XRCC4, hence we have named c9orf142—XLS (XRCC4-like small protein). Depletion of c9orf142/XLS in cells impaired DSB repair consistent with a defect in NHEJ. Furthermore, c9orf142/XLS interacted with other core NHEJ factors. These results demonstrate the existence of a new component of the NHEJ DNA repair pathway in mammalian cells.


NHEJ, non-homologous end joining; DNA-PKcs, DNA-dependent protein kinase catalytic subunit; XLF, XRCC4-like factor; XLS, XRCC4-like small protein; DSB, double-stranded DNA breaks; HR, homologous recombination; PMSF, phenylmethanesulphonyl fluoride; EtBr, ethidium bromide; IP, immunoprecipitation