REAGENT or RESOURCE	SOURCE	IDENTIFIER
Bacterial and Virus Strains
Recombinant baculovirus expressing FluPolC PB1, P3 and PB2-protein A	Bieniossek et al., 2012, Hengrung et al., 2015	N/A
Recombinant baculovirus expressing FluPolA PB1, P3 and PB2-protein A	Bieniossek et al., 2012, York et al., 2013	N/A
Chemicals, Peptides, and Recombinant Proteins
AcTEV protease	Thermo Fisher Scientific	Cat# 12575015
SuperScript III	Thermo Fisher Scientific	Cat# 18080093
pS5-CTD: Biotin-PEG-YSPTS∗PSYSPTS∗ PSYSPTS∗PSYSPTS∗PS	Cambridge Peptides; Martínez-Alonso et al., 2016	N/A
pS2-CTD: Biotin-PEG-YS∗PTSPSYS∗PTSPSYS∗ PTSPSYS∗PTSPS	Cambridge Peptides; Martínez-Alonso et al., 2016	N/A
UnP-CTD: Biotin-PEG-YSPTSPSYSPTSPSYS PTSPSYSPTSPS	Cambridge Peptides; Martínez-Alonso et al., 2016	N/A
Scr-CTD: Biotin-PEG-PSSSTPSSYTPSPSSS PTSYSPYYTSPP	Cambridge Peptides; Martínez-Alonso et al., 2016	N/A
IgG Sepharose 6 Fast Flow	GE Healthcare	Cat# 17096901
Hi-Load Superdex 200 16/60	GE Healthcare	Cat# 45-002-490
Lipofectamine 2000	Thermo Fisher Scientific	Cat# 11668027
TRI Reagent	Sigma-Aldrich	Cat# T9424
[α-32P] GTP	PerkinElmer	Cat# BLU006H250UC
Vaccinia capping system	New England Biolabs	Cat# M2080S
Deposited Data
Coordinates of pS5-CTD bound FluPolC	This paper	PDB: 6F5O
Cryo-EM map of promoter vRNA bound FluPolC	This paper	EMDB: EMD-4190
Imaging data deposited in Mendeley	This paper	https://doi.org/10.17632/tswbw8d2h7.1
Experimental Models: Cell Lines
HEK293T cells	Dunn School Cell Bank	N/A
Sf9 insect cells	Dunn School Cell Bank	N/A
Oligonucleotides
vRNA RT primer 5′-CGCAAGGCGACAA GGTGCTGA-3′	Fodor et al., 2002	N/A
m/cRNA RT primer 5′-ATGTTCTTTACGA TGCGATTGGG-3′	Fodor et al., 2002	N/A
5S rRNA RT primer 5′-ACCCTGCTTAGCTT CCGAGA-3′	Hara et al., 2006	N/A
RNA for capping (20 nt) 5′-ppAAUCUAUAAUAG CAUUAUCC-3′	Chemgenes; Hengrung et al., 2015	N/A
RNA for capping (11 nt) 5′-ppGAAUACUCAAG-3′	Chemgenes; Hengrung et al., 2015	N/A
5′ FluPolC vRNA promoter RNA 5′-AGCAGUAGCAA GGGG-3′	Dharmacon; Hengrung et al., 2015	N/A
3′ FluPolC vRNA promoter RNA 5′-CCCCUGCUU CUGCU-3′	Dharmacon; Hengrung et al., 2015	N/A
5′ FluPolA vRNA promoter RNA 5′- AGUAGAAAC AAGGCC-3′	Dharmacon; Fodor et al., 2002	N/A
3′ FluPolA vRNA promoter RNA 5′- GGCCUGCU UUUGCU-3′	Dharmacon; Fodor et al., 2002	N/A
Recombinant DNA
pHMG PB1	Donated by Nadia Naffakh; Crescenzo-Chaigne et al., 1999	N/A
pHMG PB2	Donated by Nadia Naffakh; Crescenzo-Chaigne et al., 1999	N/A
pHMG PA	Donated by Nadia Naffakh; Crescenzo-Chaigne et al., 1999	N/A
pHMG NP	Donated by Nadia Naffakh; Crescenzo-Chaigne et al., 1999	N/A
pC/PRCAT	Donated by Nadia Naffakh; Crescenzo-Chaigne et al., 1999	N/A
Software and Algorithms
Chimera 1.10.2	Pettersen et al., 2004	https://www.cgl.ucsf.edu/chimera/download.html
ResMap	Kucukelbir et al., 2014	http://resmap.sourceforge.net/
RELION (VLION)	Scheres, 2012	https://www2.mrc-lmb.cam.ac.uk/relion/index.php/Download_%26_install
EMAN2	Tang et al., 2007	http://blake.bcm.edu/emanwiki/EMAN2
Motioncor2	Zheng et al., 2017	http://msg.ucsf.edu/em/software/motioncor2.html
CryoSPARC	Punjani et al., 2017	https://v2.cryosparc.com/
GCTF	Zhang, 2016	https://www.mrc-lmb.cam.ac.uk/kzhang/Gctf/
Xia2	Winter et al., 2013	https://xia2.github.io/
PHASER	McCoy et al., 2007	http://www.phaser.cimr.cam.ac.uk/index.php/Phaser_Crystallographic_Software
COOT	Emsley and Cowtan, 2004	https://www2.mrc-lmb.cam.ac.uk/personal/pemsley/coot/
PHENIX	Adams et al., 2010	https://www.phenix-online.org/
SWISS-MODEL Oligomer server	Biasini et al., 2014	https://swissmodel.expasy.org/
Aida Image Analyzer (3.27.001)	Elysia Raytest	N/A