A genomic fragment extending from approximately 1000bp upstream of the Orc1 transcription start site through to 200bp downstream of the Orc1 transcription unit. The Orc1 coding sequence has been mutated to contain mutations in both the Walker A motif (K604A amino acid substitution) and in the Walker B motif (D684A and E685A amino acid substitutions) and is tagged at the C-terminal end with EGFP.