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Figure 9
Comparison of the U4 and U1 Sm-site heptads. (a) The U4 and U1 Sm-site heptads are superimposed and viewed from the flat face at a glancing angle. The only notable difference occurs at the sixth nucleotide, where the U123 base of U4 snRNA is bound in the pocket of SmD1, while the G130 base of U1 snRNA lies outside the central hole. The G130 base partially covers the base of U129, which is stacked on the face near G130 with His37 in L3 of SmB. Thus, shielding of UV irradiation by G130 is likely to have prevented the cross-linking of U1 snRNA to L3 of SmB (Urlaub et al., 2001 ![]() |
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