The work described below is carried out in close collaboration with the laboratory of Dr. Ron Patterson (Department of Microbiology and Molecular Genetics).
The research interests of our laboratories are focused on two carbohydrate-binding proteins, galectin-1 and galectin-3. The galectins comprise a family of galactose-binding proteins that share characteristic amino acid sequences in the carbohydrate recognition domain of the polypeptides. Our interest in this system stemmed from the observation that galectin-3 was found as a ribonucleoprotein complex in the nucleus. Using nuclear extracts derived from HeLa cells, capable of carrying out splicing of pre-mRNA in a cell-free assay, depletion and reconstitution experiments demonstrated that galectins-1 and -3 are splicing factors. More recently, we have documented that galectins-1 and -3 both independently bind to a protein designated Gemin4. The significance of this finding lies in the fact that other investigators had shown that Gemin4 is one component of a macromolecular complex, the SMN complex, that plays important roles in the biogenesis, delivery, and regeneration of small nuclear ribonucleoprotein particles (snRNPs) for spliceosome assembly. On the basis of these and other observations, the immediate objectives of our research include:
(a) to delineate and characterize the components and interactions of the ribonucleoprotein complex on which galectins-1 and -3 have been found;
(b) to define the step(s) during which galectins-1 and -3 participate in splicing;
(c) to test, by site-directed mutagenesis, whether carbohydrate-binding is required for the role of; galectins in the splicing reaction;and
(d) to study the nucleo-cytoplasmic shuttling properties of galectin-3, in terms of import and export signals and in terms of a possible role in mRNA transport.