DESCRIPTION (Adapted from applicant's description): The minibrain (Mnb) gene is located in the Down syndrome critical region of human chromosome 21. Evidence suggests that an elevated Mnb gene dosage, as in trisomy 21, contributes to Down syndrome phenotypes. The Mnb gene encodes a dual specificity tyrosine phosphorylation regulated kinase (DYRK) whose function in mammalian cells is currently unknown. The investigators plan to elucidate the cellular role of the Mnb kinase by identifying and characterizing substrates of this kinase as well as proteins that modulate its activity.