Structure and mechanism of DNA delivery of a gene transfer agent.

Alphaproteobacteria, which are the most abundant microorganisms of temperate oceans, produce phage-like particles called gene transfer agents (GTAs) that mediate lateral gene exchange. However, the mechanism by which GTAs deliver DNA into cells is unknown. Here we present the structure of the GTA of Rhodobacter capsulatus (RcGTA) and describe the conformational changes required for its DNA ejection. The structure of RcGTA resembles that of a tailed phage, but it has an oblate head shortened in the direction of the tail axis, which limits its packaging capacity to less than 4,500 base pairs of linear double-stranded DNA. The tail channel of RcGTA contains a trimer of proteins that possess features of both tape measure proteins of long-tailed phages from the family Siphoviridae and tail needle proteins of short-tailed phages from the family Podoviridae. The opening of a constriction within the RcGTA baseplate enables the ejection of DNA into bacterial periplasm.

Effects of Precise Deletions in Rhodobacter sphaeroides Reaction Center Genes on Steady-state Levels of Reaction Center Proteins: A Revised Model for Reaction Center Assembly.

Possible interactions between photosynthetic reaction center (RC) proteins that protect these membrane proteins from proteolytic digestion in RC complex assembly were evaluated by use of translationally in-frame (nonpolar) RC gene-specific deletions. The RC H, RC M and RC L proteins were produced from plasmids, either alone or in concert with one or both of the others, in a strain of Rhodobacter sphaeroides that contained chromosomal deletions of all three RC genes. The steady-state amounts of these proteins in cell membrane and soluble fractions were assessed in western blots. The data are used to propose a model of RC assembly in which the RC M protein accumulates in the cell membrane regardless of the presence of the RC H and RC L proteins, and the RC M protein is a nucleus for addition of RC L followed by RC H in assembly of the RC holocomplex.

Celebrating the millennium - historical highlights of photosynthesis research, Part 2.

This paper is an introduction to Part 2 of our celebrations of the historical highlights of photosynthesis research. Part 1 was published in October 2002 as Volume 73 of Photosynthesis Research. After a brief introduction, we recognize two giants in the field: Cornelis B. van Niel (for anoxygenic photosynthesis), and Robert Hill (for oxygenic photosynthesis). This is followed by recognition of a 1960 book by Hans Gaffron, and a multi-authored book edited by W. Ruhland and André Pirson, and inclusion in the appendix of a list of selected books. Our celebration is enhanced by the inclusion of beautiful paintings of cells by Antoinette Ryter. After introducing all the historical papers contained in this volume, we honor Louis N. M. Duysens, one of the greatest biophysicists of our time, and finally we dedicate this volume to a great scientist, humanist and peacemaker: Eugene I. Rabinowitch. [12pt] 'Annihilating all that is made To a green thought in a green shade' - Andrew Marvell (1621-1678), The Garden (1681).