Lee K Y, Hopkins J D, Syvanen M
Department of Medical Microbiology and Immunology, School of Medicine, University of California, Davis 95616.
Mol Microbiol. 1991 Aug;5(8):2039-46. doi: 10.1111/j.1365-2958.1991.tb00826.x.
A new aminoglycoside resistance gene (aphA1-IAB) confers high-level resistance to neomycin. The sequence of aphA1-IAB is closely related to aphA1 found in the transposons Tn4352, Tn903 and Tn602. For example, aphA1-IAB differs from aphA1-903 at five nucleotides that result in four amino acid replacements. The enzyme encoded by aphA1-IAB has a significantly higher turnover number with neomycin, kanamycin and G418 as substrates than does the aphA1-903 enzyme. A parsimonious phylogenetic tree suggests that aphA1-IAB evolved from an ancestral form that is closely related or identical to the aphA1 found in Tn903. The excess of replacement substitutions over silent substitutions in aphA1-IAB, as well as its convergence toward aphA3 from Staphylococcus aureus, is indicative of selective evolution. Our hypothesis to explain these results is that aphA1-IAB evolved under the selective pressure of neomycin use in relatively recent times.
一种新的氨基糖苷类抗性基因（aphA1-IAB）赋予对新霉素的高水平抗性。aphA1-IAB的序列与转座子Tn4352、Tn903和Tn602中发现的aphA1密切相关。例如，aphA1-IAB与aphA1-903在五个核苷酸上不同，这导致四个氨基酸替换。由aphA1-IAB编码的酶以新霉素、卡那霉素和G418为底物时，其周转数明显高于aphA1-903酶。一个简约系统发育树表明，aphA1-IAB从一个与Tn903中发现的aphA1密切相关或相同的祖先形式进化而来。aphA1-IAB中替换替换相对于沉默替换的过量，以及它向金黄色葡萄球菌的aphA3趋同，表明是选择性进化。我们解释这些结果的假说是，aphA1-IAB在相对较近的时期在新霉素使用的选择压力下进化而来。
