Purified elongation factor SII is sufficient to promote read-through by purified RNA polymerase II at specific termination sites in the human histone H3.3 gene.

Purified RNA polymerase II terminates transcription in vitro at sites within genes which also block transcript elongation in vivo. Studies on a termination site within the first intron of the human histone H3.3 gene have shown that transcription elongation factor SII can promote read-through at this site when the polymerase initiates transcription from a promoter in the presence of the accessory initiation factors. Using 3'-extended templates to direct specific initiation by purified RNA polymerase II, we show here that purified SII is sufficient to effect read-through of this terminator by the purified polymerase alone. Thus, the interaction of purified SII with an elongation complex containing only the polymerase, the template, and the nascent transcript can change the termination properties of RNA polymerase II and can effect read-through of a region that blocks elongation in the cell.