| Nova-1 is a neuron-specific RNA binding protein, distributed both in the nucleus and in the cytoplasm of several populations of neurons. The work presented here confirms that Nova-1 binds a sequence of RNA found in an intron of the glycine receptor α2 subunit pre-mRNA. Evidence that Nova-1 acts as a regulator of alternative splicing in transfected cell lines is presented. Furthermore, a direct role of Nova-1 on splicing is demonstrated by establishing an in vitro assay for Nova-1's regulatory role in splicing. Potential functional partners of Nova are suggested by the demonstration of physical interactions between Nova-1 and molecules whose action in the splicing machinery is well described, such as U1 70K, a protein component of U1 snRNP, and U2AF65.; The sedimentation properties of Nova in neuronal cytoplasmic extracts are consistent with the engagement of Nova in heterogeneous structures, probably mRNPs, and with polysomes, suggesting a role for Nova in the regulation of cytoplasmic phenomena of RNA metabolism, such as mRNA localization and translation. These considerations prompted a gene expression screen aimed to identify differences in the pool of mRNAs associated with heavy polysomes in wild type and Nova-1-null mice. Several genes whose mRNAs have been found to undergo changes in abundance specifically in the polysome fraction in the absence of Nova have described functional roles in post-synaptic terminal structure and functions. Nova-1 was also found to be a phospho-protein, and its phosphorylation site is in an alternative cassette exon. |
