King Michael R, Steenbergen Susan M, Vimr Eric R
Laboratory of Sialobiology, Department of Pathobiology, University of Illinois at Urbana-Champaign, Urbana, IL 61802, USA.
Trends Microbiol. 2007 May;15(5):196-202. doi: 10.1016/j.tim.2007.03.006. Epub 2007 Apr 5.
Phase variation is usually thought of as the stochastic switching between alternatively expressed ('on') and unexpressed ('off') phenotypic states. However, coupling synthesis of a monotonous homopolysaccharide to a mechanism of random but incomplete chemical modification produces almost infinite structural variation. Potentially limitless variability implies that evolution can produce highly ornate or extravagant flourishes reminiscent of the baroque style. Here, we describe an analysis of capsular polysialic acid form variation in Escherichia coli K1, demonstrating that the large number of variant structures is controlled by a single contingency locus. The mechanism for generating maximum structural diversity from maximal genetic parsimony is conferred by a simple translational switch carried on a K1-specific prophage.
相变通常被认为是交替表达的（“开启”）和未表达的（“关闭”）表型状态之间的随机切换。然而，将单调同多糖的合成与随机但不完全的化学修饰机制相结合会产生几乎无限的结构变异。潜在的无限变异性意味着进化可以产生高度华丽或奢华的装饰，让人联想到巴洛克风格。在这里，我们描述了对大肠杆菌K1中荚膜多聚唾液酸形式变异的分析，证明大量的变体结构由单个应急位点控制。从最大遗传简约性产生最大结构多样性的机制是由K1特异性原噬菌体上携带的一个简单翻译开关赋予的。
