A gene controlling condensation of heterochromatin in Drosophila melanogaster.

A temperature-sensitive lethal mutant of Drosophila melanogaster was used to identify an essential cell cycle function that is necessary for the mitotic condensation of heterochromatic but not of euchromatic portions of the genome. This mutant is an allele at a locus (mus-101) identified earlier by the use of mutagen-sensitive mutants. The data suggest that the mutagen-sensitive and repair-defective phenotypes of viable mus-101 mutants result from a disruption in chromosome organization.