My GSTP research aims to use novel mass spectrometric instrumentation to characterize histone isoforms in differentiating human embryonic stem cells. Furthermore, we hope to correlate histone modification isoforms with changes in gene expression in hopes of better understanding how histone modifications regulate transcription and differentiation. Using a modified LTQ-Orbitrap mass spectrometer, we have analyzed and quantified histone H4 isoforms in human embryonic stem cells at multiple states of differentiation, and have identified over 50 previously unknown protein isoforms. I will be interrogating gene expression associated with regions on DNA where specific isoforms of histone H4 bind. I will be using ChIP-chip analysis to idenfity genes associated with dimethylated lysine 20. In addition, I will identify and quantify changes in histone H3 with respect to differentiation.