Clarke N D
Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205.
Proc Natl Acad Sci U S A. 1994 Nov 8;91(23):11084-8. doi: 10.1073/pnas.91.23.11084.
Intervening protein sequences, called inteins, are intronlike elements that are removed posttranslationally, apparently by self-splicing. The conserved and essential residues of precursor proteins consist of an asparagine as the last residue of the intein and a hydroxyl- or thiol-containing residue immediately following both splice junctions. Evidence for a branched intermediate has been reported [Xu, M.-Q., Southworth, M., Mersha, F., Hornstra, L. & Perler, F. (1993) Cell 75, 1371-1377]; however, the chemical nature of the branched structure is unclear. I propose a mechanism that includes the formation of a branched structure, provides an explanation for the reversal of branch formation observed at high pH, and accounts for each of the essential amino acids. The branched structure is formed by nucleophilic attack of the asparagine side chain on the N-terminal splice junction. The nature of this branched structure is a distinguishing feature of the model and can be experimentally tested.
插入蛋白序列，即内含肽，是类似内含子的元件，在翻译后被去除，显然是通过自我剪接。前体蛋白的保守且必需的残基包括一个天冬酰胺作为内含肽的最后一个残基，以及紧邻两个剪接位点之后的一个含羟基或硫醇的残基。已经有关于分支中间体的报道[徐，M.-Q.，索思沃思，M.，默沙，F.，霍恩斯特拉，L. & 佩勒，F.（1993年）《细胞》75卷，1371 - 1377页]；然而，分支结构的化学性质尚不清楚。我提出了一种机制，该机制包括分支结构的形成，对在高pH下观察到的分支形成的逆转做出了解释，并说明了每个必需氨基酸的情况。分支结构是由天冬酰胺侧链对N端剪接位点的亲核攻击形成的。这种分支结构的性质是该模型的一个显著特征，并且可以通过实验进行检验。
