Inteins (intervening proteins) are proteins that perform protein-splicing posttranslational modifications  with the goal of creating a regulated Cas9; SpCas9 has been recombined with the intein 37R3-2 [69, 70].
Muir, "Inteins: nature's gift to protein chemists," Chemical Science, vol.
Either binding domains or inteins have been used to generate Cas9 with a switch response.
The chitin-binding domain (CBD) from Bacillus circulans consists of 51 amino acids, which is commonly used as tags for affinity purification of recombinant proteins in combination with self-splicing inteins in bacterial systems .
These elements are naturally self-splicing proteins called inteins that can excise themselves from the parent protein [74, 75].
Dean et al., "Protein splicing elements: inteins and exteins--a definition of terms and recommended nomenclature," Nucleic Acids Research, vol.
Topics include: transposon Tn7, mercury resistant transposons, integrons, inteins
and introns, restriction-modification systems as mobile epigenetic elements, Tn1549 and closely related elements, integrative and conjugative elements encoding DDE transposases, and the staphylococcal cassette chromosome.
Among the topics are yeast-based chemical genomic approaches, activity-based protein profiling of cys proteases, using analogue sensitive technologies to target kinases of interest, using split inteins
to prepare semi-synthetic proteins and to study the mechanisms of protein trans-splicing, and introducing chemical reporter groups by bio-orthogonal ligation reactions for imaging cell-surface glycans.
It's not yet completely clear how this unusual process occurs, but it doesn't appear to involve protein-splicing enzymes called inteins
(SN: 10/2/99, p.
Investigators now use inteins to purify proteins or bend them into loops, for example.
While biotechnology applications of inteins have blossomed, biologists have made little progress in revealing the roles that inteins naturally play inside a cell--or even if they have a cellular function at all.
Determining the purpose of inteins might have a medical payoff.