Michael R. Green
Eukaryotic Gene ExpressionWe have a broad interest in the biochemical mechanisms that regulate gene expression in eukaryotes. We pursue this interest using a variety of experimental systems and approaches that involve molecular biological, biochemical and genetic methodology. Thus, investigators in this laboratory are exposed to diverse scientific questions, systems and experimental approaches, facilitating their training as generalists.
Much of gene regulation occurs at the transcriptional level. A central question in the field is how do promoter-specific activator proteins (activators) communicate with the general transcription machinery to stimulate transcription? We have developed assays that monitor the assembly of general transcription factors onto the DNA template in response to an activator. The results of these studies have suggested models for how transcription activation occurs. Predictions of these models are then tested using in vivo systems including mammalian cells and yeast.
A second, broad question is how are transcriptional activators themselves regulated? To address this issue, we largely turn to animal viruses, which have provided important models for studying gene expression in higher eukaryotes. Many of these viruses encode regulatory proteins that redirect cellular transcription components to express viral genes. We study how such transcriptional regulators as the adenovirus E1a protein, the Tax protein of human T-cell leukemia virus (HTLV), the pX protein of Hepatitis B Virus (HBV), and the Tat protein of Human Immunodeficiency Virus (HIV) work.
In higher eukaryotes gene expression is also regulated at the post-transcriptional level. For example, by alternative processing of an mRNA precursor (pre-mRNA) multiple polypeptides can be generated from a single gene. Splicing occurs in a large multi-subunit complex, the spliceosome, the formation of which is dependent upon multiple proteins and small nuclear ribonucleoprotein proteins (snRNPs). We are particularly interested in splicing factors that act early during spliceosome assembly; these factors play a critical role in defining splice sites and are targets for splicing regulators. Through these studies we seek to understand how the specificity and accuracy of splicing is achieved, the basis of catalysis, and the mechanisms involved in alternative splicing. Another RNA processing event we are studying is the export of the fully processed mRNA from the nucleus to the cytoplasm. Again, viral regulatory proteins, such as the HIV Rev protein, provide attractive model systems.