Effects of histone tail domains on the rate of transcriptional elongation through a nucleosome

The N-terminal tail domains of the core histones play important roles in ge ne regulation, but the exact mechanisms through which they act are not know n. Recent studies suggest that the tail domains may influence the ability o f RNA polymerase to elongate through the nucleosomal DNA and, thus, that po sttranslational modification of the tail domains may provide a control poin t for gene regulation through effects on the elongation rate. We take advan tage of an experimental system that uses bacteriophage T7 RNA polymerase as a probe for aspects of nucleosome transcription that are dominated by the properties of nucleosomes themselves. With this system, experiments can ana lyze the synchronous, real-time, single-passage transcription on the nucleo somal template. Here, we use this system to directly test the hypothesis th at the tail domains may influence the "elongatability" of nucleosomal DNA a nd to identify which of the tail domains may contribute to this. The result s show that the tail domains strongly influence the rate of elongation and suggest that the effect is dominated by the N-terminal domains of the (H3-H 4)(2) tetramer. They further imply that tail-mediated octamer transfer is n ot essential for elongation through the nucleosome. Acetylation of the tail domains leads to effects on elongation that are similar to those arising f rom complete removal of the tail domains.