Schnetz K, Stülke J, Gertz S, Krüger S, Krieg M, Hecker M, Rak B
Institut für Biologie III, Albert-Ludwigs Universität, Freiburg, Germany.
J Bacteriol. 1996 Apr;178(7):1971-9. doi: 10.1128/jb.178.7.1971-1979.1996.
Gene licS of Bacillus subtilis encodes an excreted Beta-1,3-1,4-endoglucanase necessary for lichenan utilization. Upstream of licS we found a gene (termed licT) together with its promoter which encodes a transcriptional antiterminator of the BglG family. Genes licT and licS are separated by a palindromic sequence (lic-t) reminiscent of transcriptional terminators recognized by the antiterminator proteins of the BglG family. The LicT protein can prevent termination at terminator lic-t and also at terminator t2 of the Escherichia coli bgl operon and BglG prevents termination at lic-t. The role of LicT in licS regulation by preventing termination at its terminator lic-t appears to be limited since expression of licS is inducible only two- to threefold. This limited regulation is mainly due to a high basal level of licS expression which can in part be attributed to the presence of a second promoter preceding licS and located downstream of lic-t. However, disruption of gene licT leads not only to loss of inducibility of licS but also to loss of growth on lichenan or on its degradation products, indicating its stringent role in beta-glucan utilization.
枯草芽孢杆菌的基因licS编码一种分泌型β-1,3-1,4-内切葡聚糖酶，该酶是利用地衣多糖所必需的。在licS上游，我们发现了一个基因（称为licT）及其启动子，它编码BglG家族的转录抗终止子。基因licT和licS被一个回文序列（lic-t）隔开，该序列让人联想到BglG家族抗终止子蛋白所识别的转录终止子。LicT蛋白可以阻止在终止子lic-t以及大肠杆菌bgl操纵子的终止子t2处的终止，并且BglG可以阻止在lic-t处的终止。LicT通过阻止在其终止子lic-t处的终止来调控licS的作用似乎有限，因为licS的表达仅可诱导两到三倍。这种有限的调控主要是由于licS表达的基础水平较高，这部分可归因于在licS之前且位于lic-t下游存在第二个启动子。然而，基因licT的破坏不仅导致licS诱导性的丧失，还导致在地衣多糖或其降解产物上生长的丧失，表明其在β-葡聚糖利用中的严格作用。
