FIGURE 10-12 Schematic diagram of human RNA polymerase II with the CTD extended. The length of the human RNA polymerase II carboxy-terminal domain (CTD) and the linker region that connects it to the polymerase is shown relative to the globular domain of the polymerase. In its extended form, the CTD can associate with multiple RNA-processing factors simultaneously. See P. Cramer, D. A. Bushnell, and R. D. Kornberg, 2001, Science 292:1863.