CRYSTALLOGRAPHIC STUDIES OF LARGE MACROMOLECULAR ASSEMBLIES

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The projects being pursued include large macromolecular assemblies that are involved in all steps of gene expression. The first of these are components of the replisome involved in copying DNA, including the replicating DNA polymerase III, DnaB helicase and primase. Also being pursued is the structure of the clamp loader complexed with the clamp and bound to a DNA substrate. The second assembly under study is the ribosome, specifically the 50S ribosomal subunit, is to be extended to include the entire 70S ribosome in various states of the protein synthesis process. Attempts to crystallize the 70S ribosome with EF-Tu, or EF-G, or release factors are underway. Further, studies of the translating 70S ribosome in the process of secreting protein through a translocon are well along. A third assembly not related to gene expression is that of fatty acid synthase, a 2.5 million molecular weight assembly containing 8 enzyme activities, whose crystals diffract to 3.8 ¿ resolution at 24 ID. Finally, structural studies of proteins involved in transcription including initiation intermediate complexes of T7 RNA polymerase, apo-catabolite gene activator protein and E. coli RNA polymerase holoenzyme bound to a promoter DNA. These are being pursued to understand transcription initiation and its regulation in a monomeric and multisubunit enzyme.