THE K-43 GENE, REQUIRED FOR CHORION GENE AMPLIFICATION AND DIPLOID-CELL CHROMOSOME-REPLICATION, ENCODES THE DROSOPHILA HOMOLOG OF YEAST ORIGIN RECOGNITION COMPLEX SUBUNIT-2

Lethal alleles of the Drosophila k43 gene result in small or missing i maginal discs, greatly reduced mitotic index, and fragmented and abnor mally condensed chromosomes. A female-sterile allele of k43 specifical ly reduces chorion gene amplification in ovarian follicle cells. k43 w as cloned by chromosomal walking, and the identification of the k43 ge ne was confirmed by phenotypic rescue and sequence analysis of mutant alleles. The sequence analyses reveal that the k43 gene encodes the Dr osophila homolog of the yeast origin recognition complex subunit 2 (Or c2p), a protein required for replication origin function and transcrip tional silencing in yeast. These results suggest an evolutionarily con served role for Orc2p in eukaryotic chromosomal DNA replication.