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The gene transfer agent (GTA) of Rhodobacter capsulatus Lang, Andrew Stephen

Abstract

An unusual system of genetic exchange exists in the purple non-sulfur bacterium Rhodobacter capsulatus. DNA transmission is mediated by a small bacteriophage-like particle called the gene transfer agent (GTA) that transfers random 4.5 kb segments of the producing cell's genome to recipient cells, where allelic replacement occurs. This thesis presents the results of gene mutagenesis, cloning, and analysis experiments which show that GTA resembles a defective prophage related to bacteriophages from diverse genera of bacteria, that has been adopted by R. capsulatus for genetic exchange. A pair of cellular proteins, CckA and CtrA, appear to constitute part of a sensor kinase/response regulator signaling pathway that is involved in expression of GTA structural genes. This signaling pathway controls growth phase-dependent regulation of GTA gene messages, yielding maximal gene expression in the stationary phase. I suggest that GTA is an ancient prophage remnant that has evolved in concert with the bacterial genome, resulting in a genetic exchange process Controlled by the bacterial cell.

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