Screening medium: for 250 ml LB agar (for about ten plates) add 250 μl of 10 mM IPTG, 2.5 ml of 20% arabinose, 250 μl of 100 mg/ml ampicillin (100 μg/ml) and 250 μl of 35 mg/ml kanamycin (35 μg/ml).