p73 (ref. 1) has high homology with the tumour suppressor p53 (refs 2-4), as well as with p63, a gene implicated in the maintenance of epithelial stem cells. Despite the localization of the p73 gene to chromosome 1p36.3, a region of frequent aberration in a wide range of human cancers, and the ability of p73 to transactivate p53 target genes, it is unclear whether p73 functions as a tumour suppressor. Here we show that mice functionally deficient for all p73 isoforms exhibit profound defects, including hippocampal dysgenesis, hydrocephalus, chronic infections and inflammation, as well as abnormalities in pheromone sensory pathways. In contrast to p53-deficient mice, however, those lacking p73 show no increased susceptibility to spontaneous tumorigenesis. We report the mechanistic basis of the hippocampal dysgenesis and the loss of pheromone responses, and show that new, potentially dominant-negative, p73 variants are the predominant expression products of this gene in developing and adult tissues. Our data suggest that there is a marked divergence in the physiological functions of the p53 family members, and reveal unique roles for p73 in neurogenesis, sensory pathways and homeostatic control.

Mutations in the p53 tumor suppressor gene are the most frequent genetic alterations found in human cancers. Recent identification of two human homologues of p53 has raised the prospect of functional interactions between family members via a conserved oligomerization domain. Here we report in vitro and in vivo analysis of homo-and hetero-oligomerization of p53 and its homologues, p63 and p73. The oligomerization domains of p63 and p73 can independently fold into stable homotetramers, as previously observed for p53. However, the oligomerization domain of p53 does not associate with that of either p73 or p63, even when p53 is in 15-fold excess. On the other hand, the oligomerization domains of p63 and p73 are able to weakly associate with one another in vitro. In vivo co-transfection assays of the ability of p53 and its homologues to activate reporter genes showed that a DNA-binding mutant of p53 was not able to act in a dominant negative manner over wildtype p73 or p63 but that a p73 mutant could inhibit the activity of wild-type p63. These data suggest that mutant p53 in cancer cells will not interact with endogenous or exogenous p63 or p73 via their respective oligomerization domains. It also establishes that the multiple isoforms of p63 as well as those of p73 are capable of interacting via their common oligomerization domain.Tumor suppressor p53 is a transcriptional regulator of genes involved in control of the cell cycle and/or apoptosis (reviewed in Refs. 1-3). In response to cellular stress, particularly DNA damage, p53 protein levels rise, leading to changes in expression of p53 responsive genes and subsequent cell cycle arrest and/or apoptosis. Growth arrest or cell death prevents damaged DNA from being replicated and suggests a role for p53 in maintaining the integrity of the genome (4). This DNA damage checkpoint activity is central to its role as a tumor suppressor and also of major importance in the response of many cancers to conventional therapies that trigger apoptosis by damaging DNA. Inactivation of p53 through deletion, mutation, or interaction with cellular or viral proteins is a key step in over half of all human cancers (5, 6). Reactivation of the p53 pathway leading to apoptosis in cancer cells containing inactive p53 could greatly improve current modes of treatment (7,8) and could potentially be a treatment modality in itself (9, 10).Recently, two p53 homologues have been identified that can activate some of the same target genes as p53 and can induce apoptosis. The existence of these new proteins adds new complexity to our understanding of the p53 pathway and offers new potential for its reactivation in cancer cells. Human p73 (11, 12) and p63 (13-15) share regions of homology with the activation, DNA-binding, and oligomerization domains of p53. This raises the possibility of physical, and/or genetic interactions between p53 family members (13), as is often the case within other families of transcription factors such as the homeodomain proteins (16) or the Myc superfamily (17). Both p63 a...

Although it has been established that the processing factors involved in pre-mRNA splicing and 3′-end formation can influence each other positively, the molecular basis of this coupling interaction was not known. Stimulation of pre-mRNA splicing by an adjacentcis-linked cleavage and polyadenylation site in HeLa cell nuclear extract is shown to occur at an early step in splicing, the binding of U2AF 65 to the pyrimidine tract of the intron 3′ splice site. The carboxyl terminus of poly(A) polymerase (PAP) previously has been implicated indirectly in the coupling process. We demonstrate that a fusion protein containing the 20 carboxy-terminal amino acids of PAP, when tethered downstream of an intron, increases splicing efficiency and, like the entire 3′-end formation machinery, stimulates U2AF 65 binding to the intron. The carboxy-terminal domain of PAP makes a direct and specific interaction with residues 17–47 of U2AF 65, implicating this interaction in the coupling of splicing and 3′-end formation.