SNAP output for PDB entry 6go7 [SNAP web server]

PDB-id

6go7; SNAP-derived features in text and JSON formats; DNAproDB

Class

DNA binding protein

Method

X-ray (2.55 Å)

Summary

Tdt chimera (loop1 of pol mu) - full DNA synapsis complex

Reference

Loc'h J, Gerodimos CA, Rosario S, Tekpinar M, Lieber MR, Delarue M (2019): "Structural evidence for an intransbase selection mechanism involving Loop1 in polymerase mu at an NHEJ double-strand break junction." J.Biol.Chem., 294, 10579-10595. doi: 10.1074/jbc.RA119.008739.

Abstract

Eukaryotic DNA polymerase (Pol) X family members such as Pol μ and terminal deoxynucleotidyl transferase (TdT) are important components for the nonhomologous DNA end-joining (NHEJ) pathway. TdT participates in a specialized version of NHEJ, V(D)J recombination. It has primarily nontemplated polymerase activity but can take instructions across strands from the downstream dsDNA, and both activities are highly dependent on a structural element called Loop1. However, it is unclear whether Pol μ follows the same mechanism, because the structure of its Loop1 is disordered in available structures. Here, we used a chimeric TdT harboring Loop1 of Pol μ that recapitulated the functional properties of Pol μ in ligation experiments. We solved three crystal structures of this TdT chimera bound to several DNA substrates at 1.96-2.55 Å resolutions, including a full DNA double-strand break (DSB) synapsis. We then modeled the full Pol μ sequence in the context of one these complexes. The atomic structure of an NHEJ junction with a Pol X construct that mimics Pol μ in a reconstituted system explained the distinctive properties of Pol μ compared with TdT. The structure suggested a mechanism of base selection relying on Loop1 and taking instructions via the in trans templating base independently of the primer strand. We conclude that our atomic-level structural observations represent a paradigm shift for the mechanism of base selection in the Pol X family of DNA polymerases.