22. 4 The U6 spliceosome contains snrNas Figure 22.12 06-04 pairing is incompatible with 06-02 pairin U4 When U6 joins the spliceosome it is paired with 04. Release of U4 allows a conformational change in U6, one part of the released sequence forms a hairpin(dark grey), and the other part(black) Catalytic center pairs with 02. Because an adjacent region of U2 is already U6 paired with the branch site, this brings U6 into juxtaposition with UGAUcA the branch. Note that the A CUA G U2 substrate RNa is reversed from Au GU GUAGUa the usual orientation and is exon 2GA A U shown3￠-5￠ U G exon 13 请莘大 3(right) splice site branch site 5(left)splice siteFigure 22.12 U6-U4 pairing is incompatible with U6-U2 pairing. When U6 joins the spliceosome it is paired with U4. Release of U4 allows a conformational change in U6; one part of the released sequence forms a hairpin (dark grey), and the other part (black) pairs with U2. Because an adjacent region of U2 is already paired with the branch site, this brings U6 into juxtaposition with the branch. Note that the substrate RNA is reversed from the usual orientation and is shown 3￠ -5￠. 22.4 The spliceosome contains snRNAs