Interaction of the mediator head module with RNA polymerase II.

Mediator, a large (21 polypeptides, MW ∼1 MDa) complex conserved throughout eukaryotes, plays an essential role in control of gene expression by conveying regulatory signals that influence the activity of the preinitiation complex. However, the precise mode of interaction between Mediator and RNA polymerase II (RNAPII), and the mechanism of regulation by Mediator remain elusive. We used cryo-electron microscopy and reconstituted in vitro transcription assays to characterize a transcriptionally-active complex including the Mediator Head module and components of a minimum preinitiation complex (RNAPII, TFIIF, TFIIB, TBP, and promoter DNA).

Structure of the hDmc1-ssDNA filament reveals the principles of its architecture.

In eukaryotes, meiotic recombination is a major source of genetic diversity, but its defects in humans lead to abnormalities such as Down's, Klinefelter's and other syndromes. Human Dmc1 (hDmc1), a RecA/Rad51 homologue, is a recombinase that plays a crucial role in faithful chromosome segregation during meiosis. The initial step of homologous recombination occurs when hDmc1 forms a filament on single-stranded (ss) DNA.

Interaction between subunit C (Vma5p) of the yeast vacuolar ATPase and the stalk of the C-depleted V(1) ATPase from Manduca sexta midgut.

Projection maps of a V(1)-Vma5p hybrid complex, composed of subunit C (Vma5p) of Saccharomyces cerevisiae V-ATPase and the C-depleted V(1) from Manduca sexta, were determined from single particle electron microscopy. V(1)-Vma5p consists of a headpiece and an elongated wedgelike stalk with a 2.1x3.

Structural characterization of an ATPase active F1-/V1 -ATPase (alpha3beta3EG) hybrid complex.

Co-reconstitution of subunits E and G of the yeast V-ATPase and the alpha and beta subunits of the F(1)-ATPase from the thermophilic Bacillus PS3 (TF(1)) resulted in an alpha(3)beta(3)EG hybrid complex showing 53% of the ATPase activity of TF(1). The alpha(3)beta(3)EG oligomer was characterized by electron microscopy. By processing 40,000 single particle projections, averaged two-dimensional projections at 1.

Structure and subunit arrangement of the A-type ATP synthase complex from the archaeon Methanococcus jannaschii visualized by electron microscopy.

In Archaea, bacteria, and eukarya, ATP provides metabolic energy for energy-dependent processes. It is synthesized by enzymes known as A-type or F-type ATP synthase, which are the smallest rotatory engines in nature (Yoshida, M., Muneyuki, E.