Tetramerization and interdomain flexibility of the replication initiation controller YabA enables simultaneous binding to multiple partners

YabA negatively regulates initiation of DNA replication in low-GC Gram-positive bacteria. The protein exerts its control through interactions with the initiator protein DnaA and the sliding clamp DnaN. Here, we combined X-ray crystallography, X-ray scattering (SAXS), modeling and biophysical approaches, with in vivo experimental data to gain insight into YabA function. The crystal structure of the N-terminal domain (NTD) of YabA solved at 2.7 Å resolution reveals an extended α-helix that contributes to an intermolecular four-helix bundle. Homology modeling and biochemical analysis indicates that the C-terminal domain (CTD) of YabA is a small Zn-binding domain. Multi-angle light scattering and SAXS demonstrate that YabA is a tetramer in which the CTDs are independent and connected to the N-terminal four-helix bundle via flexible linkers. While YabA can simultaneously interact with both DnaA and DnaN, we found that an isolated CTD can bind to either DnaA or DnaN, individually. Site-directed mutagenesis and yeast-two hybrid assays identified DnaA and DnaN binding sites on the YabA CTD that partially overlap and point to a mutually exclusive mode of interaction. Our study defines YabA as a novel structural hub and explains how the protein tetramer uses independent CTDs to bind multiple partners to orchestrate replication initiation in the bacterial cell.     

AChemS: the beginning. Association for Chemoreception Sciences

This paper unfolds the events, the people and the times that led up to the founding of AChemS and fashioned its character during its early formative years. It describes the path over which AChemS came, going from the original assertions and denials for the need of such an organization to its later inception and nascent development. This narration highlights such topics as the debate over the need for AChemS, the role of National Science Foundation in the founding of AChemS, the derivation of the Association's name, the choice of Sarasota and the Hyatt House as the meeting site, the generation of the programs for the early annual meetings, the adoption of the bylaws, the process of incorporation and tax deferment, and the birth of the Givaudan Lectureship. Most emphatically highlighted, however, is the enthusiasm, commitment and hard work that the members of the chemosensory research community displayed in bringing AChemS to fruition.