Interaction of RNA polymerase II with structurally altered nucleosomal particles. Transcription is facilitated by loss of one H2A.H2B dimer.

The loss of one H2A.H2B dimer from the nucleosomal core increases its affinity for RNA polymerase II and its efficiency as a transcription template, allowing transcription of the entire DNA present in the particle. In contrast, the nucleosomal core lacking the amino-terminal ends of histones, which has an affinity for polymerase equal to that of the H2A.H2B-deficient core, shows transcription properties similar to those of the whole nucleosomal core, with synthesis of short RNA chains (40 nucleotides or less). Similar results were obtained with a bacterial RNA polymerase. The improved efficiency of the H2A.H2B-deficient cores as transcription templates does not appear to be produced by nonspecific loss of protein or structural relaxation of the particle. These results suggest that a particle lacking one H2A.H2B dimer might be a necessary intermediate during in vivo transcription.