Saxena I M, Kudlicka K, Okuda K, Brown R M
Department of Botany, University of Texas at Austin 78713-7640.
J Bacteriol. 1994 Sep;176(18):5735-52. doi: 10.1128/jb.176.18.5735-5752.1994.
The synthesis of an extracellular ribbon of cellulose in the bacterium Acetobacter xylinum takes place from linearly arranged, membrane-localized, cellulose-synthesizing and extrusion complexes that direct the coupled steps of polymerization and crystallization. To identify the different components involved in this process, we isolated an Acetobacter cellulose-synthesizing (acs) operon from this bacterium. Analysis of DNA sequence shows the presence of three genes in the acs operon, in which the first gene (acsAB) codes for a polypeptide with a molecular mass of 168 kDa, which was identified as the cellulose synthase. A single base change in the previously reported DNA sequence of this gene, resulting in a frameshift and synthesis of a larger protein, is described in the present paper, along with the sequences of the other two genes (acsC and acsD). The requirement of the acs operon genes for cellulose production was determined using site-determined TnphoA/Kanr GenBlock insertion mutants. Mutant analysis showed that while the acsAB and acsC genes were essential for cellulose production in vivo, the acsD mutant produced reduced amounts of two cellulose allomorphs (cellulose I and cellulose II), suggesting that the acsD gene is involved in cellulose crystallization. The role of the acs operon genes in determining the linear array of intramembranous particles, which are believed to be sites of cellulose synthesis, was investigated for the different mutants; however, this arrangement was observed only in cells that actively produced cellulose microfibrils, suggesting that it may be influenced by the crystallization of the nascent glucan chains.
木醋杆菌中细胞外纤维素带的合成是由线性排列、位于膜上的纤维素合成与挤出复合体完成的，这些复合体指导聚合和结晶的耦合步骤。为了鉴定该过程中涉及的不同组分，我们从这种细菌中分离出了一个木醋杆菌纤维素合成（acs）操纵子。DNA序列分析表明acs操纵子中有三个基因，其中第一个基因（acsAB）编码一种分子量为168 kDa的多肽，该多肽被鉴定为纤维素合酶。本文描述了该基因先前报道的DNA序列中的一个单碱基变化，该变化导致移码并合成了一个更大的蛋白质，同时还给出了另外两个基因（acsC和acsD）的序列。使用位点定向的TnphoA/Kanr基因阻断插入突变体确定了acs操纵子基因对纤维素产生的需求。突变分析表明，虽然acsAB和acsC基因对于体内纤维素的产生至关重要，但acsD突变体产生的两种纤维素同质多晶型物（纤维素I和纤维素II）的量减少，这表明acsD基因参与纤维素结晶。针对不同的突变体研究了acs操纵子基因在确定被认为是纤维素合成位点的膜内颗粒线性排列中的作用；然而，这种排列仅在积极产生纤维素微纤丝的细胞中观察到，这表明它可能受新生葡聚糖链结晶的影响。
