Nuclear factors in sevenless signalling.

Recent studies in both vertebrates and invertebrates support all 'hourglass' model for signal transduction from receptor tyrosine kilnases: Ras channels signals front diverse receptor tyrosine kinases into a common cytoplasmic kinase cascade, the targets of which are an even more diverse collection of nuclear proteins. What are these nuclear factors, and bow do they interact to direct specific cellular responses to a generic signal? The past year has brought considerable progress in our quest to answer these questions in one model genetic system, the Drosophila eye.