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Figure 1.
Fig. 1. a, schematic diagram of the chemical mechanism
for protein splicing. The four-step reaction couples the
excision of the intein (red) from the precursor protein with the
ligation of the two exteins (blue and blue-green) via a native
peptide bond. b, diagram of the new motif structure of PI-SceI
according to Pietrokovski (9). Blocks N1-N4 and C1 and C2 (blue)
contain residues involved in protein splicing; blocks EN1-EN4
(black) contain residues associated with the endonuclease/linker
domain. Nucleophilic residues are highlighted below the block
diagram (yellow letters in purple box), and highly conserved
residues are shown in red. c, sequence alignment of the
wild-type PI-SceI (VMA) and mutant miniprecursor ( VMA29). The
red dash and arrow illustrate the N- and C-terminal splicing
sites. Red residues in the VMA29 sequence indicate mutations
made to the wild-type sequence (blue). Cys1 and Asn454 were
mutated to Ala in order to block in vivo protein splicing.
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