Fig. 1. Phosphorylation state of the RPB1 subunit in Xenopus embryos. Batches of ten unfertilised eggs (0) or embryos fertilised and allowed to develop at 16°C were sampled, lysed at the indicated time (hours post fertilisation, h.p.f.) and electrophoresed along with a whole lysate from A6 cells (A6). The RNAPII largest subunit was detected by western blot using the POL3/3 antibody. The positions of the IIa, IIo and IIe forms are indicated.