Figure 2.

Mapping of active site residues and human pathogenic mutations in the model of the human CTD and linker region. (A) Residues directly important for NTP hydrolysis, including the arginine finger (R609), the putative base stack (F621) and others (K607, F610 and F628) (Matsushima et al., 2008) are shown in red, sphere representation; the loops important for DNA-binding in the CTD of T7 gp4 (Notarnicola et al., 1995; Singleton et al., 2000; Washington et al., 1996) are shown in blue, cartoon representation; and the human disease-related residues (Appendix Table 1) are shown in sphere representation and colored according to their proposed functional properties including subunit interactions (cyan), NTP hydrolysis (yellow) and DNA-binding (dark blue). R391 (dark gray) has not been given a functional assignment (see text for details). (B) Representation of the juxtaposition of two protomers (light and dark green, cartoon representation), highlighting the NTP-binding site (circled) and the subunit interaction region (boxed). (C) Closer view of the subunit interaction region, showing the human disease-related residues in stick representation (see color version of this figure at www.informahealthcare.com/bmg).