Margolis N, Hogan D, Tilly K, Rosa P A
Laboratory of Microbial Structure and Function, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, Hamilton, Montana 59840.
J Bacteriol. 1994 Nov;176(21):6427-32. doi: 10.1128/jb.176.21.6427-6432.1994.
The Lyme disease spirochete Borrelia burgdorferi must survive in both its tick vector and its mammalian host to be maintained in nature. We have identified the B. burgdorferi guaA gene encoding GMP synthetase, an enzyme involved in de novo purine biosynthesis that is important for the survival of bacteria in mammalian blood. This gene encodes a functional product that will complement an Escherichia coli GMP synthetase mutant. The gene is located on a 26-kb circular plasmid, adjacent to and divergent from the gene encoding the outer surface protein C (OspC). The guaB gene homolog encoding IMP dehydrogenase, another enzyme in the purine biosynthetic pathway, is adjacent to guaA. In Borrelia hermsii, a tick-borne relapsing fever spirochete, the guaA and guaB genes are located on a linear plasmid. These are the first genes encoding proteins of known function to be mapped to a borrelial plasmid and the only example of genes encoding enzymes involved in the de novo purine biosynthesis pathway to be mapped to a plasmid in any organism. The unique plasmid location of these and perhaps other housekeeping genes may be a consequence of the segmented genomes in borreliae and reflect the need to adapt to both the arthropod and mammalian environments.
莱姆病螺旋体伯氏疏螺旋体必须在其蜱传播媒介和哺乳动物宿主中都能存活，才能在自然界中得以维持。我们已经鉴定出伯氏疏螺旋体的guaA基因，该基因编码GMP合成酶，这是一种参与嘌呤从头生物合成的酶，对细菌在哺乳动物血液中的存活至关重要。该基因编码一种功能性产物，可互补大肠杆菌GMP合成酶突变体。该基因位于一个26 kb的环状质粒上，与编码外表面蛋白C（OspC）的基因相邻且转录方向相反。编码嘌呤生物合成途径中的另一种酶IMP脱氢酶的guaB基因同源物与guaA相邻。在蜱传回归热螺旋体赫氏疏螺旋体中，guaA和guaB基因位于一个线性质粒上。这些是首批被定位到疏螺旋体质粒上的编码已知功能蛋白质的基因，也是在任何生物体中编码参与嘌呤从头生物合成途径的酶的基因被定位到质粒上的唯一例子。这些基因以及可能其他管家基因在质粒上的独特定位，可能是疏螺旋体基因组呈片段化的结果，反映了适应节肢动物和哺乳动物两种环境的需求。
