Localization of EGFP-Twi1p. The loxP-EGFP-TWI1 strain #1 (Fig. 4B) was mated with the wild-type B2086 and localization of EGFP-Twi1p at conjugation stages E1 (A, B), E2 (C), M1 (D) or L1 (E, F) was observed using fluorescence microscopy. A detailed illustration of conjugation stages can be found in . DNA was counterstained by DAPI. a: macronucleus, i: micronucleus, na: new macronucleus, pa: parental macronucleus.