THE INHIBITOR OF DNA-REPLICATION ENCODED BY THE DROSOPHILA GENE PLUTONIUM IS A SMALL, ANKYRIN REPEAT PROTEIN

The plutonium (plu) gene product controls DNA replication early in Dro sophila development. plu mutant females lay unfertilized eggs that hav e undergone extensive DNA synthesis. In fertilized embryos from plu mu tant mothers, S-phase is uncoupled from mitosis. The gene is expressed only in ovaries and embryos, null alleles are strict maternal effect mutations, and the phenotype of inappropriate DNA replication is the c onsequence of loss-of-gene function. plu therefore negatively regulate s S-phase at a time in early development when commitment to S-phase do es not depend on cyclic transcription. plu encodes a protein with two ankyrin-like repeats, a domain for protein - protein interaction. plu is immediately adjacent to, but distinct from, the PCNA gene.