Zulty J J, Barcak G J
Department of Biological Chemistry, University of Maryland School of Medicine, Baltimore 21201, USA.
Proc Natl Acad Sci U S A. 1995 Apr 11;92(8):3616-20. doi: 10.1073/pnas.92.8.3616.
DNA sequencing, RNA mapping, and protein expression experiments revealed the presence of a gene, tfoX+, encoding a 24.9-kDa polypeptide, that is transcribed divergently from a common promoter region with the Haemophilus influenzae rec-1+ gene. H. influenzae strains mutant for tfoX failed to bind transforming DNA and were transformation deficient. Primer extension experiments utilizing in vivo total RNA from precompetent and competent H. influenzae cells demonstrated that transcription of tfoX+ increased immediately upon competence induction, suggesting that tfoX+ is an early competence gene. Similar experiments showed that the expression of the late competence-specific gene, com101A+, was tfoX+ dependent. Moreover, expression of plasmid-borne tfoX+ in H. influenzae resulted in constitutive competence. The addition of cyclic adenosine monophosphate (cAMP) to strains carrying a tfoX::lacZ operon fusion resulted in an immediate increase in beta-galactosidase activity that correlated with an increase in genetic transformability. Collectively, our results suggest that TfoX may play a key role in the development of genetic competence by regulating the expression of late competence-specific genes.
DNA测序、RNA定位和蛋白质表达实验表明，存在一个名为tfoX+的基因，它编码一种24.9 kDa的多肽，该基因与流感嗜血杆菌rec-1+基因从共同的启动子区域反向转录。tfoX基因发生突变的流感嗜血杆菌菌株无法结合转化DNA，且转化能力存在缺陷。利用处于感受态前期和感受态的流感嗜血杆菌细胞的体内总RNA进行引物延伸实验表明，tfoX+的转录在感受态诱导后立即增加，这表明tfoX+是一个早期感受态基因。类似的实验表明，晚期感受态特异性基因com101A+的表达依赖于tfoX+。此外，在流感嗜血杆菌中表达质粒携带的tfoX+会导致组成型感受态。向携带tfoX::lacZ操纵子融合的菌株中添加环磷酸腺苷（cAMP）会导致β-半乳糖苷酶活性立即增加，这与遗传转化能力增加相关。总体而言，我们的结果表明，TfoX可能通过调节晚期感受态特异性基因的表达在遗传感受态的发展中发挥关键作用。
