Clark M A, Baumann L, Baumann P
Department of Microbiology, University of California, Davis 95616-8665.
Curr Microbiol. 1992 Nov;25(5):283-90. doi: 10.1007/BF01575863.
The aphid Schizaphis graminum is dependent on an association with a prokaryotic endosymbiont (Buchnera aphidicola). The nucleotide (nt) sequence of a 5040 base pair (bp) DNA fragment of B. aphidicola, homologous to the rplL-rpoB-rpoC portion of the Escherichia coli beta operon, was determined. The DNA coded for the terminal 35 amino acids of RplL (large ribosomal subunit protein L7/L12), the complete RpoB (beta-subunit of RNA polymerase), and the first 209 amino acids of RpoC (beta'-subunit of RNA polymerase). The deduced sequences of B. aphidicola RplL, RpoB, and RpoC were 71, 84, and 91% identical, respectively, to the homologous proteins of E. coli. The sequences of two portions of the intergenic region between rplL and rpoB were nearly identical in both B. aphidicola and E. coli. One sequence constituted an inverted repeat that could be an RNase III-messenger RNA processing site; the other sequence preceded RpoB. A compilation of the codon usage for RpoB, RpoC, and other B. aphidicola proteins indicated a major preference for A or T in the first and third positions, a result consistent with the low guanine plus cytosine (G + C) content of the DNA of this organism.
蚜虫麦二叉蚜依赖于与一种原核内共生体（蚜虫内共生菌）的共生关系。测定了蚜虫内共生菌一段5040个碱基对（bp）DNA片段的核苷酸（nt）序列，该片段与大肠杆菌β操纵子的rplL - rpoB - rpoC部分同源。该DNA编码RplL（大核糖体亚基蛋白L7/L12）的末端35个氨基酸、完整的RpoB（RNA聚合酶的β亚基）以及RpoC（RNA聚合酶的β'亚基）的前209个氨基酸。蚜虫内共生菌RplL、RpoB和RpoC的推导序列分别与大肠杆菌的同源蛋白有71%、84%和91%的同一性。在蚜虫内共生菌和大肠杆菌中，rplL和rpoB之间基因间区域的两个部分序列几乎相同。一个序列构成一个反向重复，可能是一个RNase III - 信使RNA加工位点；另一个序列位于RpoB之前。对RpoB、RpoC和其他蚜虫内共生菌蛋白的密码子使用情况的汇编表明，在第一和第三位置主要偏好A或T，这一结果与该生物DNA的低鸟嘌呤加胞嘧啶（G + C）含量一致。
