N-terminal EGFP-tagging of TWI1 using Cre/loxP system. (A) A scheme of induction of Cre-mediated loxP recombination and selection of loxP-EGFP-TWI1 cells. See text for details. (B) loxP excision analysis by PCR. Total genomic DNA was extracted from 13 presumptive loxP-EGFP-TWI1 strains and analyzed by PCR using the primers shown in Fig. 3A. The products corresponding to the non-excised loxP-neo4-loxP-EGFP-TWI1 locus (+neo4) and the excised loxP-EGFP-TWI1 locus (-neo4) are marked by arrows.