My research interests are focused on the regulation of gene activity in animal cells, in particular regulation of gene expression during the cell cycle by postranscriptional mechanisms. One system we study is the regulation of histone mRNA, both during the mammalian cell cycle and during early development in frogs and sea urchins. Histone mRNAs are the only mRNAs that do not have polyA tails, ending instead in a conserved stem-loop structure. Histone mRNAs are present only in S-phase cells and most of the regulation is mediated by the 3′ end of histone mRNA. Histone genes lack introns, and histone mRNA is formed by a single processing reaction, cleavage to form the 3′ end of the histone mRNA. The mRNA is then immediately transported to the cytoplasm. Both the cleavage reaction to form histone mRNA and the half-life of the histone mRNA are regulated during the cell cycle. We have cloned the cDNA for the stem-loop binding protein (SLBP) that binds the 3′ end of histone mRNA and participates in all aspects of histone mRNA metabolism. SLBP is a critical factor involved in regulating histone mRNA levels. Our current interests are in understanding how SLBP carries out its multiple functions; RNA binding, 3′ processing, transport, stimulator of translation and regulating histone mRNA half-life. In addition, we are studying how SLBP itself is regulated and how this regulation connects the other cell cycle regulators with the regulation of histone mRNA.
In embryos which undergo a very rapid series of cell divisions after fertilization, there is an exponentially increasing demand for histones to assemble the newly replicated DNA into chromatin. During this time the histone mRNAs are not cell-cycle regulated but are stable for multiple cell cycles. We have cloned embryo specific SLBPs from these stages and are determining how they function to regulate histone mRNA metabolism in frog and sea urchin embryos. We are also studying the role of the G1 cyclins, cyclin D and cyclin E in the regulation of these early cell cycles that lack gap phases.