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Nucleic Acids Res. 2001 May 15;29(10):E47.

New variants of inducible Cre recombinase: a novel mutant of Cre-PR fusion protein exhibits enhanced sensitivity and an expanded range of inducibility.

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Institute for Genetics, University of Cologne, Weyertal 121, D-50931 Cologne, Germany.


We have developed a novel inducible Cre mutant with enhanced recombinase activity to mediate genetic switching events. The protein, designated Cre*PR, is composed of a new Cre mutant at the N-terminus followed by the ligand-binding domain (LBD) of the progesterone receptor (PR). The response to low doses of inducer is significantly enhanced by elongating the C-terminus of the PR LBD from amino acid 891 to 914. The mutant Cre lacks the first 18 amino acids and contains a Val-->Ala substitution at position 336, thereby destroying a cryptic splice donor at the 3'-end of CRE: The latter mutation reduces unwanted background recombinase activity in the absence of the synthetic ligand RU486 by a factor of at least 10 to an almost undetectable level. Thus, the recombinase activity turns out to be inducible by a factor of >200. We expect Cre*PR to serve as a valuable tool for conditional expression of genes both in vitro and in vivo.

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