Fig. 3. Role for Np73 in apoptosis. This diagram depicts a role for Np73 in neuronal apoptosis. The level of Np73, the predominant form of p73 in certain developing neurons, is highest when maintained in NGF (left side of diagram). After NGF withdrawal (- NGF), Np73 levels decrease and cells undergo p53-dependent apoptosis. The possible mechanism(s) by which Np73 may inhibit p53 activities include: (1) occupying of p53 DNA-binding sites (gray rectangles); and (2) hetero-oligomerization of N forms with wild-type p53. A similar model has been proposed for Np63 during UV-induced apoptosis in keratinocytes (discussed in text).