Steinmetz M, Le Coq D, Aymerich S, Gonzy-Tréboul G, Gay P
Mol Gen Genet. 1985;200(2):220-8. doi: 10.1007/BF00425427.
We present the sequence of a 2 kb fragment of the Bacillus subtilis Marburg genome containing sacB, the structural gene of levansucrase, a secreted enzyme inducible by sucrose. The peptide sequence deduced for the secreted enzyme is very similar to that directly determined by Delfour (1981) for levansucrase of the non-Marburg strain BS5. The peptide sequence is preceded by a 29 amino acid signal peptide. Codon usage in sacB is rather different from that in the sequenced genes of other secreted enzymes in B. subtilis, especially alpha-amylase. Genetic evidence has shown that the sacB promotor is rather far from the beginning of sacB (200 bp or more). The 200 bp region preceding sacB shows some of the features of an attenuator. A preliminary discussion of the putative workings and roles of this attenuator-like structure is proposed. sacRc mutations, which allow constitutive expression of levansucrase, have been located within the 450 bp upstream of sacB. It is shown that sacRc and sacR+ alleles control in cis the expression of the adjacent sacB gene.
我们展示了枯草芽孢杆菌马尔堡菌株基因组中一个2 kb片段的序列，该片段包含果聚糖蔗糖酶的结构基因sacB，果聚糖蔗糖酶是一种可被蔗糖诱导分泌的酶。推导得到的该分泌酶的肽序列与德尔富尔（1981年）直接测定的非马尔堡菌株BS5的果聚糖蔗糖酶的肽序列非常相似。该肽序列之前有一个29个氨基酸的信号肽。sacB中的密码子使用情况与枯草芽孢杆菌中其他分泌酶（尤其是α-淀粉酶）的已测序基因中的密码子使用情况有很大不同。遗传证据表明，sacB启动子距离sacB起始位置相当远（200 bp或更远）。sacB之前的200 bp区域显示出一些弱化子特征。本文对这种类似弱化子结构的假定作用和功能进行了初步讨论。允许果聚糖蔗糖酶组成型表达的sacRc突变位于sacB上游450 bp范围内。结果表明，sacRc和sacR +等位基因顺式控制相邻sacB基因的表达。
