PROTEIN SPLICING - AN ANALYSIS OF THE BRANCHED INTERMEDIATE AND ITS RESOLUTION BY SUCCINIMIDE FORMATION

Protein splicing involves the excision of an internal domain from a pr ecursor protein and the ligation of the external domains so as to gene rate two new proteins. Study of this process has recently been facilit ated by the isolation of a precursor and a branched intermediate from a thermophilic protein splicing element expressed in a foreign protein context. Two aspects of protein splicing are examined in this paper. We demonstrate a succinimide at the C-terminus of the spliced internal protein, implicating cyclization of asparagine in resolution of the b ranched intermediate, and we identify an alkali-labile bond in the bra nched intermediate. A revised protein splicing model based on these ex perimental results is presented.