Polypeptide set to be used in light dependent gene recombination

A set of two polypeptides, which comprises

• a first polypeptide comprising an N-terminal side fragment of a Cre protein, said Cre protein having the amino acid sequence SEQ ID NO:
• 1 and a second polypeptide comprising a C-terminal side fragment of the Cre protein, wherein:
• the N-terminal side fragment and the C-terminal side fragment are cleavage products resulting from cleavage between amino acid positions 59 and 68 or 101 and 111 of SEQ ID NO:
• 1;
• the N-terminal side fragment is linked, at its C-terminal amino acid, to a first protein;
• the C-terminal side fragment is linked, at its N-terminal amino acid, to a second protein;
• said first and second proteins light-dependently form a dimer;
• and
• the first and second proteins each independently comprise a polypeptide comprising the amino acid sequence of SEQ ID NO:
• 2 or a variant of the amino acid sequence of SEQ ID NO:
• 2 with amino acid substitutions at positions 52 and 55;
• positions 52, 55, and 85;
• positions 52, 55, 74, and 85;
• or positions 52, 55, 135, and 165.