Processing and metabolism of RNA in eukaryotes.
Dr. Steven's laboratory is interested in the structure and function of ribonucleoproteins, in particular, the small nuclear ribonucleoproteins (snRNPs) involved in processing pre-mRNA. There are a number of snRNPs in all eukaryotic cells, some highly conserved, others which seem to be specific to a group of organisms. The splicing of pre-mRNA occurs in the context of the spliceosome, a 4-5 megadalton complex which contains the pre-mRNA, five snRNAs (U1, U2, U4, U5 and U6) and over 70 proteins. There are many varieties of spliceosomal snRNPs in the eukaryotic nucleus. In yeast, there are three abundant mono-snRNPs - the U1 snRNP, the U5 snRNP and the U6 snRNP. There is a very small amount of a di-snRNP called U4/U6, more of a tri-snRNP called U4/U6•U5 and novel snRNPs he recently identified which participate directly in the splicing reaction. These new snRNPs are termed the tetra-snRNP (U2•U4/U6•U5) and the penta-snRNP (U1•U2•U4/U6•U5) (See Stevens et al. Mol. Cell (2002)).
Utilizing many techniques, such as yeast genetics, affinity chromatography, mass spectrometry, biochemistry and structural analysis, the overarching goal of this laboratory is to determine how ribonucleoproteins assemble, how they communicate with their substrate(s), how they undergo the drastic rearrangements they often do and how they disassemble to start the cycle over again.
In addition to the ribonucleoproteins involved in pre-mRNA splicing, other snRNPs from yeast and human cells are being analyzed to determine their composition, assayed for function and their structures being determined by electron cryo-microscopy and X-Ray diffraction.