Ph.D., Yale, 1983

Associate Professor

Department of Cell Biology and Molecular Genetics

University of Maryland

College Park, MD 20742

Phone: (301)-405-6934

E-mail: smount@umd.edu

Research Interests: Molecular Genetics.

I and my coworkers seek to understand how multicellular organisms accomplish the correct processing of RNA from protein-coding genes. This involves identifying the elements of primary sequence information that determine where (and whether or not) splicing will occur, determining which components of the splicing machinery play especially salient roles in recognizing those signals, and determining how those factors act. Our research exploits powerful techniques of molecular genetics provided by the fruit fly Drosophila melanogaster. We are currently focused on B52 and U1 70K, two factors that function in splice site selection.

Earlier screens for mutations in genes that play key roles in RNA processing decisions led to the isolation of B52ED, a dominant mutation in B52, the gene for an essential SR protein splicing factor. This dominant mutation is a single amino acid change in the RNA-binding domain that results in increased affinity for several RNAs. Enhanced RNA-binding provides a unique opportunity to demonstrate and probe the role of RNA-binding by SR proteins in the faithful selection of splice sites in vivo. We are pursuing this approach by studying effects on the processing of RNA from target genes such as doublesex and Ultrabithorax, whose phenotypic expression is altered in the B52^ED allele.

We are also exploiting mutations in the gene for U1 70K, a protein component of the U1 small nuclear ribonucleoprotein. Like B52, U1 70K is highly conserved, and is known to participate in the early stages of splicing, when splice selection is accomplished. Lethal loss-of-function alleles and wild type transgenes exist for both proteins, and ongoing research exploits both genetic and biochemical approaches. Biochemical approaches include the study of splicing (including partial splicing reactions such as the formation of prespliceosomal complexes) in extracts from flies carrying mutant forms of these proteins, or in extracts that have been depleted of these proteins exploiting epitope-tagged transgenes. It is important to note that there is every indication that Drosophila will serve as an excellent and general model for pre-mRNA splicing in many multicellular animals.

In addition, we are examining the effect of mutations in, or rearrangements of, splicing signals. Selected mutations are constructed in Drosophila introns or their flanking exons, and the effects of these mutations are then assessed in vivo (by transfection of Drosophila cell lines and by germline transformation of whole flies) and in vitro (by splicing in nuclear extracts, and by biochemical analysis of spliceosome assembly).

Representative Publications:

Mount, S. M. 1997. Genetic depletion reveals an essential role for an SR protein splicing factor in vertebrate cells. Bioessays 19: 189-192.

Mount, S. M. 1996. AT-AC Introns: An ATtACk on dogma. (Perspectives) Science271: 1690-1692.

Guo, M. and S. M. Mount. 1995. Localization of sequences required for size-specific splicing of a small Drosophila intron in vitro. J. Mol. Biol. 253: 426-437.

Mount, S. M., X. Peng and E. Meier. 1995. Some nasty little facts to bear in mind when predicting splice sites. DIMACs Gene-finding and Gene Structure Prediction Workshop. Philadelphia.

Peng, X. and S. M. Mount. 1995. Genetic enhancement of RNA-processing defects by a dominant mutation in B52, the Drosophila gene for an SR protein splicing factor. Mol. Cell. Biol. 15: 6273-6282.

Kurkulos, M., J. M. Weinberg, D. Roy, and S.M. Mount. 1994. P element mediated in vivo deletion analysis of white-apricot: deletions between direct repeats are strongly favored. Genetics 136: 1001-1011.

Lo, P., D. Roy, and S. M. Mount. 1994. Suppressor U1 snRNAs in Drosophila melanogaster. Genetics 138: 365-378.

Guo, M., P. C. H. Lo and S.M. Mount. 1993. Species-specific signals for the splicing of a short Drosophila intron in vitro. Mol. Cell. Biol. 13: 1104-1118.

Mount, S.M., C. Burks, G. Stormo, J. Hertz and C. Fields. 1992. Splicing signals in Drosophila: intron size, information content, and consensus sequences. Nucleic Acids Res. 20: 4255-4262.