| Over the past century, we have witnessed a tremendous growth in our understanding of the inheritance and regulation of genetic information. Novel biochemical, molecular and cytological approaches have been instrumental in furthering our understanding of DNA structure and function. What is now clear is that the underlying processes involving DNA are far more complicated that originally envisioned. In fact, it is often ignored that all cellular processes involving DNA are not performed on naked DNA but rather in the context of histones and higher-order chromatin structure. In turn, mechanisms regulating chromatin structure, such as posttranslational histone modifications, have far reaching implications for replication, transcription, DNA repair, apoptosis and mitosis and as a corollary, tumorigenesis.; A major focus of this thesis has been to develop novel in situ approaches to investigate the dynamics of posttranslational histone modifications and the substrate specificity preference profiles of enzymes regulating their dynamics. The results described in this thesis focus primarily on the characterization of histone methylation and phosphorylation dynamics and the substrate specificity preferences of two highly related histone acetyltransferases (HATs). We document previously uncharacterized cell cycle associated dynamics of several specific methylations occurring in histones H3 and H4 and establish that one specific modification is critical for genomic integrity. Next, we identify and characterize a previously unrecognized population of phosphorylated H2AX foci that are independent of DNA DSB repair. We identify mitosis-associated dynamics for these foci that are regulated by functional ATM expression. Finally, we demonstrate that CBP and P300 exhibit subtle differences in their HAT specificity preferences, which may account for the recent functional differences ascribed to each. We propose that the complex regulation and dynamics of many posttranslational histone modifications are critical to many nuclear processes, particularly to the fidelity of mitosis. |
