The purpose of this project is to isolate three human genes, whose products are necessary for the progression of animal cells through the cell cycle. It will be accomplished by using human genomic DNA to transfect three cell cycle specific temperature sensitive mutant cell lines derived from Syrian hamster cells. The human genes will then be isolated from appropriate genomic libraries constructed from secondary or tertiary transformants. The isolation and characterization of these three genes (and their cDNA's) is important not only in itself, but also because it can give us valuable indicating on the types of genes involved in cell cycle progression.