Elizabeth Grayhack, Ph.D.

Thus, the ORFs themselves or their protein products are esponsible for these large differences in expression. Analysis of this collection has led to the two projects described below.

The roles of codons in gene expression and regulation: Although accurate and efficient translation of mRNA into proteins is crucially important for the cell, not all of the 61 codons that specify insertion of amino acids into nascent polypeptides behave equally in this process. In fact, almost all synonymous codons, i.e. those that specify the same amino acid, are used at very different frequencies within most organisms, including the yeast S. cerevisiae Although codon use has been implicated as a determinant of expression levels, neither the identity, nor the defining characteristics of codons that impair expression are known. Studies in the Grayhack laboratory are designed to define the rules and mechanisms by which specific codons, and arrangements of codons, impair gene expression, and to identify regulatory models dictated by codon usage in the yeast genome.

Developing yeast to express protein complexes for structural analysis: The structures of many eukaryotic proteins and protein complexes are still unknown because many eukaryotic proteins are either not soluble in E. coli or bear post-translational modifications that are not added in E. coli. To this end we developed a general solution to incorporate selenomethionine into proteins expressed in this yeast, for use in MAD phasing. In addition, we have developed vectors for simultaneous high level expression and affinity purification of protein complexes from S. cerevisiae. Our current goal is to explore the limits of protein expression, solubility and folding to learn in part how yeast differs from E. coli, and what factors contribute most to gene expression.

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