Wang H, Dowds B C
Department of Biology, St. Patrick's College, Maynooth, County Kildare, Ireland.
J Bacteriol. 1993 Mar;175(6):1665-73. doi: 10.1128/jb.175.6.1665-1673.1993.
The phenomenon of phase variation in the insect-pathogenic bacterium Xenorhabdus luminescens was investigated. Differential activity of the lipase enzyme (EC 3.1.1.3) was observed between the two phases of the bacteria. The enzyme was found to be secreted into the culture medium, and about five to six times greater specific activity was secreted by the primary phase than by the secondary form. The lipase gene (lip-1) was cloned and sequenced. The data imply that there is only a single Tween 80-utilizing lipase gene in X. luminescens K122. The sequence revealed a translation product of 645 amino acids, from which a hydrophobic leader sequence of 24 amino acids is removed during processing. The structure of the gene was shown to be the same in the primary and secondary forms of X. luminescens. In addition, transcription was found to start at the same position, 169 bp upstream of the translation initiation codon, in the two forms of the bacteria. Equal amounts of lipase RNA accumulated in the two forms, and at least as much lipase protein was secreted by the secondary form as by the primary. This suggests that the difference in specific activity between the enzymes secreted by the two phases probably arises from a posttranslational type of regulation.
对昆虫致病细菌发光光杆状菌中的相变现象进行了研究。在该细菌的两个阶段之间观察到脂肪酶（EC 3.1.1.3）的活性差异。发现该酶分泌到培养基中，初级阶段分泌的比活大约是次级形式的五到六倍。克隆并测序了脂肪酶基因（lip-1）。数据表明，发光光杆状菌K122中只有一个利用吐温80的脂肪酶基因。该序列揭示了一个由645个氨基酸组成的翻译产物，在加工过程中会去除一个由24个氨基酸组成的疏水前导序列。发光光杆状菌初级和次级形式的基因结构显示相同。此外，发现转录在两种细菌形式中都从翻译起始密码子上游169 bp处的相同位置开始。两种形式中积累的脂肪酶RNA量相等，次级形式分泌的脂肪酶蛋白至少与初级形式一样多。这表明两个阶段分泌的酶之间比活的差异可能源于翻译后类型的调控。
