Key resources table.

Reagent type (species) or resource	Designation	Source or reference	Identifiers	Additional information
Strain, strain background (E. coli)	Rosetta 2 (DE3)	Novagen	Cat# 71,400	Chemically competent
Antibody	anti-poly (ADP) ribose polymer (mouse monoclonal)	Abcam	Cat# ab14459, RRID:AB_301239	WB (1:500)
Antibody	Mouse IgG, HRP-linked whole Ab (from sheep)	Cytiva	Cat# NA931, RRID:AB_772210	WB (1:5000)
Recombinant DNA reagent	Human ALC1fl (16-879) pNIC-CH2 (plasmid)	Lehmann et al., 2017		UniProt ID Q86WJ1
Recombinant DNA reagent	Human ALC1cat (16-612) pNIC-CH2 (plasmid)	Lehmann et al., 2017		UniProt ID Q86WJ1
Recombinant DNA reagent	Human ALC1macro (613-879) pNIC-CH2 (plasmid)	Lehmann et al., 2017		UniProt ID Q86WJ1
Recombinant DNA reagent	Human HPF1 (1–346) pET28a (plasmid)	Gaullier et al., 2020		UniProt ID Q9NWY4
Recombinant DNA reagent	Human PARP1 (1–1014) pET28a (plasmid)	Langelier et al., 2017		UniProt ID P09874
Recombinant DNA reagent	Human PARP2 Isoform 2 (1-570) pET28a (plasmid)	GenScript		UniProt ID Q9UGN5
Software, algorithm	RELION-3.1.1	Zivanov et al., 2018	RRID:SCR_016274	https://www3.mrc-lmb.cam.ac.uk/relion/index.php/Main_Page
Software, algorithm	UCSF MotionCor2 version 1.3.2	Zheng et al., 2017		https://emcore.ucsf.edu/ucsf-software
Software, algorithm	CTFFIND4 version 4.1.9	Rohou and Grigorieff, 2015	RRID:SCR_016732	https://grigoriefflab.umassmed.edu/ctffind4
Software, algorithm	Topaz version 0.2.4	Bepler et al., 2019		https://github.com/tbepler/topaz, Tristan, 2021
Software, algorithm	cryoSPARC version 3.2	Punjani et al., 2017	RRID:SCR_016501	https://cryosparc.com/
Software, algorithm	cryoDRGN version 0.3.2	Zhong et al., 2021		https://github.com/zhonge/cryodrgn, Ellen, 2021
Software, algorithm	UCSF ChimeraX 1.1	Goddard et al., 2018	RRID:SCR_015872	https://www.rbvi.ucsf.edu/chimerax/
Software, algorithm	ISOLDE 1.1	Croll, 2018		https://isolde.cimr.cam.ac.uk/
Software, algorithm	Phenix version 1.19.2–4158	Liebschner et al., 2019	RRID:SCR_014224	https://www.phenix-online.org/