DeShazer D, Wood G E, Friedman R L
Department of Microbiology and Immunology, University of Arizona, Tucson 85724, USA.
J Bacteriol. 1995 Jul;177(13):3801-7. doi: 10.1128/jb.177.13.3801-3807.1995.
Transcription of the pertussis toxin operon (ptx) is positively regulated in Bordetella pertussis by the bvgAS locus. However, a ptx-lacZ transcriptional fusion in Escherichia coli cannot be activated by bvgAS in trans. This suggests that an additional factor(s) is required for transcription of ptx. A gene encoding a Bvg accessory factor (Baf) was identified by its ability to activate an E. coli ptx-lacZ fusion in the presence of bvgAS. The expression of ptx-lacZ was decreased by the addition of 40 mM MgSO4, a compound that also modulates ptx expression in B. pertussis. Baf alone did not activate expression of an E. coli fhaB-lacZ fusion, nor did it increase expression of fhaB-lacZ in trans with bvgAS. The gene encoding Baf was localized, sequenced, and found to produce a novel 28-kDa protein. Sequences homologous to B. pertussis baf were identified in Bordetella bronchiseptica and Bordetella parapertussis but not in Bordetella avium. When an additional copy of baf was integrated into the chromosome of BC75, a B. pertussis mutant that produces a low level of pertussis toxin, pertussis toxin production was partially complemented in the cointegrate strain.
百日咳毒素操纵子（ptx）的转录在百日咳博德特氏菌中受到bvgAS位点的正向调控。然而，大肠杆菌中的ptx - lacZ转录融合体不能被反式的bvgAS激活。这表明ptx转录需要一个额外的因子。通过在bvgAS存在的情况下激活大肠杆菌ptx - lacZ融合体的能力，鉴定出了一个编码Bvg辅助因子（Baf）的基因。添加40 mM MgSO4会降低ptx - lacZ的表达，MgSO4也是一种能调节百日咳博德特氏菌中ptx表达的化合物。单独的Baf不能激活大肠杆菌fhaB - lacZ融合体的表达，在与bvgAS反式作用时也不会增加fhaB - lacZ的表达。编码Baf的基因被定位、测序，发现其产生一种新的28 kDa蛋白。在支气管败血博德特氏菌和副百日咳博德特氏菌中鉴定出了与百日咳博德特氏菌baf同源的序列，但在鸟博德特氏菌中未发现。当将额外的baf拷贝整合到BC75（一种产生低水平百日咳毒素的百日咳博德特氏菌突变体）的染色体中时，共整合菌株中的百日咳毒素产生得到了部分互补。
