LARGE-SCALE SYNCHRONOUS MATING AND THE STUDY OF MACRONUCLEAR DEVELOPMENT IN EUPLOTES-CRASSUS

After conjugation in hypotrichous ciliates, a new macronucleus is produced from a copy of the micronucleus. This transformation involves large-scale reorganization of DNA, with conversion of the chromosomal micronuclear genome into short, gene-sized DNA molecules in the macronucleus. To study directly the changes that occur during this process, techniques were developed for synchronous mating of large populations of the hypotrichous ciliate E. crassus. The micronuclear chromosomes are polytenized during the first 20 h of macronuclear development. The polytene chromosomes lack the band-interband organization observed in othe hypotrichs and in the Diptera. Polytenization is followed by transectioning of the chromosomes. DNA was isolated at various times of macronuclear development and the average MW of the DNA decreases at the time of chromosome transectioning. A small size group of macronuclear DNA molecules (450-550 base pairs) is excised from the chromosomal DNA .apprx. 10 h later in macronuclear development.