DNA end-joining in extracts from human cells

DNA end-joining is a central feature of several DNA recombination processes. A DNA end-joining activity present in extracts prepared from cells of the human SupT1 lymphocyte cell line was characterised. Joining of blunt ends and ends having complementary single-strand extensions (SSEs) were precise with no insertion or deletion of substrate base pairs. DNA sequencing analysis showed that molecules having non complementary ends of the same polarity, or molecules having one blunt end and one end with a SSE, were joined without loss of nucleotide sequences in the double-stranded region of the substrate molecule. The joining patterns observed have several features that are consistent with DNA end-joining activities previously observed in vitro in extracts from Xenopus eggs and in vivo in mammalian cells and yeast.