CHROMATIN REMODELING DURING LIVER DEVELOPMENT

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The primary aim of this proposal is to examine the processes whereby the sequential binding of developmentally regulated transcription factors organizes the cis-acting sequences which make up the enhancer of the serum albumin gene into a series of three translationally phased nucleosome-like particles encompassing the essential enhancer factor binding sites in liver chromatin. This will be accomplished using three different approaches. First, the assembly of the albumin enhancer into an active higher-order nucleoprotein complex during liver development will be followed by comparison of nucleosome phasing at the albumin enhancer in liver chromatin at successive developmental stages. These observations will be combined with recently completed in vivo DMS protection analyses which have identified the transcription factors responsible for activating the albumin enhancer. Second, the ability of purified transcription factors alone and in combination to bind to and perturb nucleosomes reconstituted in vitro from albumin enhancer fragments and core histones will be determined, in order to determine the mechanisms whereby transcription factors specify the nucleosome structure of the albumin enhancer. Finally, the role played by specific transcription factors in the chromatin remodeling of the albumin enhancer will be assessed by studying the activity and chromatin structure of albumin enhancer transgenes containing mutations in selected enhancer binding sites during liver development in transgenic mice. These studies should further our understanding of the role played by chromatin architecture in transcriptional regulation as well as lend insight into the mechanisms whereby regulatory factors dictate normal liver growth and development.