um Gus2 G+C,G+CG+G i R; s2 s3 R R ls3 1 1 RR R RR R Rus2十 RRaist R2+Rs R+Rs R+R3 或表示为： um azus2 ajus3 ais =州+9+4R1 i s1 R2 us2 R3 us3 i2 i3 + – + – 1 2 3 1 2 3 3 3 2 3 2 2 1 G G i G G G u G G G u u S S S n + + + + + = 或表示为： (3) 1 (2) 1 (1) 1 1 2 2 3 3 1 1 n n n n s S S u u u u a u a u a i = + + = + + 2 3 2 3 1 2 3 2 3 2 3 3 2 2 3 1 2 3 3 3 2 3 2 2 1 1 1 1 1 1 1 1 R R R R i R R R u R R R u R R i R R u R R R u R S S S S S S + + + + + = + + + + + =