A novel murine gene, designated ayk1, which encodes a putative serine/threonine kinase has been cloned and characterized. The predicted catalytic domain of the protein is highly similar to that of Drosophila aurora (62.9% identity), and to that of Saccharomyces Ipl1 (49.4% identity). All three proteins also have very basic calculated isoelectric points (higher than 10). aurora has been recently shown to be crucial for centrosome separation and chromosome segregation, while Ipl1 is essential for yeast viability and accurate chromosome segregation. The results of Northern analysis and in situ RNA localization support a similar role for ayk1. The gene is specifically expressed in meiotically active cells, and during spermatogenesis, ayk1 transcripts accumulate just before the first meiotic division. Much lower levels are found in mitotically active cells. We propose that Ayk1, aurora and Ipl1 belong to a distinct new subfamily of kinases. These results suggest that the pathways controlling chromosome segregation are evolutionary conserved, and that similar control mechanisms operate in mitosis and meiosis.