Seminars Archive

Structural studies of eukaryotic and archaeal transcription

Abstract
The message written in the genes needs to be read and interpreted The first step in this process is called transcription, in which the DNA sequence of a gene is copied into a template made of RNA. This step is carried out by a very complex and tightly regulated molecular apparatus. A variety of proteins and transcription factors regulate gene expression, allowing cells to adapt, differentiate and respond to environmental stimuli. The enzymes at the core of this process are the RNA polymerases: a detailed knowledge of their structure and function is therefore a pre-requisite to our understanding of the molecular mechanisms of gene expression. To elucidate the architecture of RNA polymerase we have investigated the three-dimensional structures of various RNA polymerase subunits. The eukaryotic subunits Rpb4 and Rpb7 form a heterodimer that reversibly associates with the RNAPII 10-subunits core. We determined the crystal structure of the complex between the Methanococcus jannaschii subunits E and F, the archaeal homologues of Rpb7 and Rpb4 and proposed a model for the interactions between Rpb4/Rpb7 and the core RNAP in which the RNA binding face of Rpb7 is positioned to interact with the nascent RNA transcript. We recently determined the crystal structure of the human Rpb4/Rpb7 heterodimer to 2.6 Ã… resolution. To dissect the RNA binding properties of the E/F and Rpb4/Rpb7, we made a number of point-mutants and identified a putative RNA binding path which is conserved in evolution. The E/F structure also suggested an intriguing and previously undetected homology between the RNA polymerase II Rpb4/Rpb7 complex and RN polymerase I subunits A14 and A43. We have recently obtained crystals of the yeast A14/A43 heterodimer.