Table 3.

Overall Rmsd for Mutant and Native Methionine Sites from all Four Particles

Residue/Site	Number of Atoms	SD from the Mean (Å)
L9M	4	1.4
I19M	4	1.2
E31M	4	1.3
I41M	4	1.9
I49M	3	1.9
E61M	4	1.4
I75M	4	1.6
M67	27	2.5
M88	29	1.6
M134	32	1.1
M157	31	1.2

Three matrices were generated for the superposition of U1-70k selenium sites from U1 snRNP complexes B, C, and D onto the U1-70k selenium sites of complex A, using the program O (Jones et al., 1991). An SD from the mean was then calculated for each site from the transformed coordinates.

$$SD=\sqrt{\frac{1}{n}·\sum _{i=1}^n{\left(\overline{x}-x_i\right)}^2+{\left(\overline{y}-y_i\right)}^2+{\left(\overline{z}-z_i\right)}^2}$$