Figure 1.
Nucleosomes containing Sin mutant histones or lacking amino-terminal tails provide a reduced barrier to traversal by polymerase II. (A) Nucleosomes were assembled on the 603 template using wild-type (n/x) or tailless (g/x) H2A/H2B, and wild-type (x/n) or Sin mutant H3 and H4. RNA in yeast polymerase II complexes was initially pulse-labelled and then extended at the indicated KCl concentrations with excess unlabelled NTPs. The locations of the nucleosome (oval), the nucleosome dyad (square), the main pol II pause sites and the position of the run-off transcript are shown. (B) As in (A), except that human pol II was used. KCl concentrations, sarkosyl addition (1%) and no-chase controls (nc) are indicated. (C) As in (B), except that the template was 603R. g, globular; H3, histone H3; H4, histone H4; n, native; pol II, polymerase II.