Epigenetics is the study of non‐genetic components that alter gene expression. One of the most notable examples is the chemical posttranslational modification of the DNA‐associated histone proteins. For my project, we focused on the effects of phosphorylation of threonine 45 on histone H3 by the STK38 kinase. In order to do this, we carried out a number of techniques: Western blotting of extracts from synchronized cells showed that the phosphorylation of H3 threonine 45 peaks at the G1/S transition of the cell cycle. Using Polymerase Chain Reaction (PCR)‐based Site‐directed Mutagenesis, we mutated a plasmid encoding wild‐type H3 into plasmids with Alanine (pET‐H3 T45A) and Glutamic Acid (pET‐H3 T45D) substitutions at threonine 45. Alanine eliminates phosphorylation while the negative charge on glutamic acid mimics the effects of threonine 45 when it is phosphorylated. We will now use these mutants to determine whether STK38 phosphorylates additional sites on histone H3 in vitro, and to immunoprecipitate histone H3 in its non‐phosphorylated and phospho‐mimic forms in vivo. This will allow us to determine whether phosphorylation at threonine 45 alters histone H3 binding proteins. From, current results we hypothesize that phosphorylation of threonine 45 plays an important role in the cell cycle, possibly having impact in the choice of whether or not the cell divides. In completing this study more will be known about how epigenetics can affect the cell cycle and more knowledge can be accessed about how histones and their modifications affect nucleosomes.Grant Funding Source: Supported by Howard Hughes Medical Institute