Newby Meredith I, Greenbaum Nancy L
Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306-4390, USA.
Nat Struct Biol. 2002 Dec;9(12):958-65. doi: 10.1038/nsb873.
Pairing of a consensus sequence of the precursor (pre)-mRNA intron with a short region of the U2 small nuclear (sn)RNA during assembly of the eukaryotic spliceosome results in formation of a complementary helix of seven base pairs with a single unpaired adenosine residue. The 2' OH of this adenosine, called the branch site, brings about nucleophilic attack at the pre-mRNA 5' splice site in the first step of splicing. Another feature of this pairing is the phylogenetic conservation of a pseudouridine (psi) residue in U2 snRNA nearly opposite the branch site. We show that the presence of this psi in the pre-mRNA branch-site helix of Saccharomyces cerevisiae induces a dramatically altered architectural landscape compared with that of its unmodified counterpart. The psi-induced structure places the nucleophile in an accessible position for the first step of splicing.
在真核生物剪接体组装过程中，前体（pre）-mRNA内含子的共有序列与U2小核（sn）RNA的一个短区域配对，导致形成一个具有七个碱基对且有一个未配对腺苷残基的互补螺旋。这个腺苷的2'-OH，称为分支位点，在剪接的第一步中对pre-mRNA的5'剪接位点进行亲核攻击。这种配对的另一个特征是U2 snRNA中一个假尿苷（ψ）残基在系统发育上几乎与分支位点相对保守。我们表明，与未修饰的对应物相比，酿酒酵母pre-mRNA分支位点螺旋中这种ψ的存在会导致显著改变的结构格局。ψ诱导的结构将亲核试剂置于剪接第一步可接近的位置。
