Embryo lysates were prepared from wild type (N2) or sig-7(n5037) mutants rescued by a sig-7::GFP::3XFLAG transgene, using either normal salt (150 mM NaCl; odd lanes) or high salt (420 mM NaCl; even lanes) extraction conditions. RNA Pol II was immunoprecipitated (IP) using an antibody that recognizes all isoforms (anti-AMA-1), and the IP material was probed by western blot using the antibodies indicated. 5% input was used for SDS-PAGE. The blots were also probed with anti-actin both to normalize for the amount of total protein used for the IP (bottom panel, lanes 1–4) and to determine the specificity of the co-IP (bottom panel; lanes 5–8). The expected sizes of the proteins assayed are as follows: SIG-7::3XFLAG::GFP, 84 KD; AMA-1 (phosphorylated), 210–250 KD; Actin, 42 KD.