Small molecule splicing modifiers have been previously described that target the general splicing machinery and thus have low specificity for individual genes. Several potent molecules correcting the splicing deficit of the SMN2 (survival of motor neuron 2) gene have been identified and these molecules are moving towards a potential therapy for spinal muscular atrophy (SMA). Here by using a combination of RNA splicing, transcription, and protein chemistry techniques, we show that these molecules directly bind to two distinct sites of the SMN2 pre-mRNA, thereby stabilizing a yet unidentified ribonucleoprotein (RNP) complex that is critical to the specificity of these small molecules for SMN2 over other genes. In addition to the therapeutic potential of these molecules for treatment of SMA, our work has wide-ranging implications in understanding how small molecules can interact with specific quaternary RNA structures.

A novel member of the poly(ADP-ribose) polymerase (PARP) family, hPARP-3,is identified here as a core component of the centrosome. hPARP-3 is preferentially localized to the daughter centriole throughout the cell cycle. The N-terminal domain (54 amino acids) of hPARP-3 is responsible for its centrosomal localization. Full-length hPAPR-3 (540 amino acids, with an apparent mass of 67 kDa) synthesizes ADP-ribose polymers during its automodification. Overexpression of hPARP-3 or its N-terminal domain does not influence centrosomal duplication or amplification but interferes with the G1/S cell cycle progression. PARP-1 also resides for part of the cell cycle in the centrosome and interacts with hPARP-3. The presence of both PARP-1 and PARP-3 at the centrosome may link the DNA damage surveillance network to the mitotic fidelity checkpoint.

We have shown that bovine spleen NAD ؉ glycohydrolase (EC 3.2.2.5), purified to homogeneity, is a multifunctional enzyme. A time-dependent formation of cADPR from NAD ؉ that did not exceed 1.5-2% of the reaction products was measurable. The cyclase activity of this enzyme was, however, best evidenced by its transformation of NGD ؉ into cyclic GDP-ribose (cGDPR). The formation of the cyclic compound could be monitored spectroscopically (UV and fluorescence) and by highperformance liquid chromatography; the product ratio of cGDPR/GDP-ribose was 2:1. Bovine spleen NAD ؉ glycohydrolase is also able to hydrolyze cADPR ( Cyclic ADP-ribose, which was originally discovered in sea urchin eggs, is thought to be the endogenous regulator of the Ca 2ϩ -induced Ca 2ϩ