Polytene chromosomes and nucleic acid metabolism during macronuclear development in Euplotes

Polytene chromosomes in two species of Euplotes, E. woodruffi and E. eurystomus, have been described during the macronuclear development following conjugation. In these two species, the giant chromosomes appear briefly in the macronuclear anlagen and disappear completely later. DNA synthesis begins concomitantly with the appearance of the giant chromosomes and reaches a peak at the maximum stage of polyteny. Shortly thereafter DNA begins to break down and the breakdown products leave the macronuclear anlagen, reducing the DNA content in the anlagen to the amount present at the earlier stages of the polytene development of the chromosomes. A later phase of DNA synthesis occurs in the anlagen with the appearance of replication bands comparable to the bands which double the DNA in the somatic macronucleus. These replication bands initiate several rounds of DNA synthesis which finally lead to the development of the vegetative macronucleus. RNA synthesis occurs uniformly on the giant chromosomes and no special RNA producing puffs or other regions are noticed on them.Research supported by American Cancer Society grant E 434 to David M. Prescott and by the Deutsche Forschungsgemeinschaft to Dieter Ammermann.