In Drosophila, the maternally expressed mei-41 and grp genes are required f
or successful execution of the nuclear division cycles of early embryogenes
is. In fission yeast, genes encoding similar kinases (rad3 and chk1, respec
tively) are components of a cell cycle checkpoint that delays mitosis by in
hibitory phosphorylation of Cdk1. We have identified mutations in a gene en
coding a Cdk1 inhibitory kinase, Drosophila wee1 (Dwee1). Like mei-41 and g
rp, Dwee1 is zygotically dispensable but is required maternally for complet
ing the embryonic nuclear cycles. The arrest phenotype of Dwee1 mutants, as
well as genetic interactions between Dwee1, grp, and mei-41 mutations, sug
gest that Dwee1 is functioning in the same regulatory pathway as these gene
s. These findings imply that inhibitory phosphorylation of Cdk1 by Dwee1 is
required for proper regulation of the early syncytial cycles of embryogene
sis.