Studies on sevenless and bride of sevenless genes have revealed that the R8 cell plays a key role in the fate of the R7 photoreceptor cell, presenting on its surface an inductive cue to which R7 responds. sev-independent induction of R7 cells has been reported in the seven-up mutation, which appears to transform R1 and R6 cells to R7 cells. We have induced recessive mutations in a gene pokkuri (pok; pokkuri is a Japanese word that means "dropping dead") that lead to overproduction of R7 cells with rather minor effects on outer photoreceptors and R8 cells. Pok protein may function as a transcription factor, as the predicted amino acid sequence contains a region similar to the consensus established for the E-26-specific (Ets) domain.