In accordance with the present invention, there are provided selection
systems and methods for screening for agents that control splicing of
inteins in their native host protein (extein) or in homologous exteins.
Specifically, there are provided positive genetic selection systems for
the screening of agents which inhibit or activate protein splicing which
comprise: a host cell containing a chromosomal gene encoding either a
drug-resistant form of a target enzyme or a wild-type target enzyme, and a
plasmid-borne gene encoding either a drug-sensitive form of the target
enzyme, which is dominantly cytotoxic upon interaction with the drug, or a
dominantly cytotoxic form of the target enzyme. In these systems the
plasmid-borne gene contains an intein, and the inhibition or activation of
splicing of the dominant cytotoxic form of the target enzyme by a given
reagent results in the survival or death of the host cell. More
specifically, positive genetic selection systems which utilize the M.
xenopi GyrA intein or M. tuberculosis DnaB helicase intein are provided.
Similar reporter systems utilizing native or homologous exteins and
systems utilizing controllable inteins are provided, as are methods of
controlling in vivo expression of proteins by modulating protein splicing
with inhibiting or activating agents, and methods of controlling the
delivery of proteinaceous drugs in vivo by modulating protein splicing.
