Restoration of wild-type p53 expression triggers cell death and eliminates tumors in vivo. The identification of mutant p53-reactivating small molecules such as PRIMA-1 opens possibilities for the development of more efficient anticancer drugs. Although the biological effects of PRIMA-1 are well demonstrated, little is known about its molecular mechanism of action. We show here that PRIMA-1 is converted to compounds that form adducts with thiols in mutant p53. Covalent modification of mutant p53 per se is sufficient to induce apoptosis in tumor cells. These findings might facilitate the design of more potent and specific mutant p53-targeting anticancer drugs.

G protein-coupled receptors (GPCRs) allosterically activate heterotrimeric G proteins and trigger GDP release. Given that there are ∼800 human GPCRs and 16 different Gα genes, this raises the question of whether a universal allosteric mechanism governs Gα activation. Here we show that different GPCRs interact with and activate Gα proteins through a highly conserved mechanism. Comparison of Gα with the small G protein Ras reveals how the evolution of short segments that undergo disorder-to-order transitions can decouple regions important for allosteric activation from receptor binding specificity. This might explain how the GPCR-Gα system diversified rapidly, while conserving the allosteric activation mechanism.

Centrioles are cylindrical, ninefold symmetrical structures with peripheral triplet microtubules strictly required to template cilia and flagella. The highly conserved protein SAS-6 constitutes the center of the cartwheel assembly that scaffolds centrioles early in their biogenesis. We determined the x-ray structure of the amino-terminal domain of SAS-6 from zebrafish, and we show that recombinant SAS-6 self-associates in vitro into assemblies that resemble cartwheel centers. Point mutations are consistent with the notion that centriole formation in vivo depends on the interactions that define the self-assemblies observed here. Thus, these interactions are probably essential to the structural organization of cartwheel centers.