The smallest known intein, found in the ribonucleoside diphosphate reductase gene of
Methanobacterium thermoautotrophicum (Mth RIR1 intein), was found to splice poorly in
Escherichia coli with the naturally occurring proline residue adjacent to the N-terminal
cysteine of the intein. Splicing proficiency increased when this proline was replaced with an
alanine residue. However, constructs that displayed efficient N-and C-terminal cleavage
were created by replacing either the C-terminal asparagine or N-terminal cysteine of the …