IDENTIFICATION AND SEQUENCES OF THE TREPONEMA-PALLIDUM MGLA AND MGLC GENES

Treponema pallidum, the agent of syphilis, cannot be continuously cult ivated in vitro. To identify treponemal genes encoding exported protei ns, we performed TnphoA mutagenesis of a T. pallidum genomic DNA libra ry in Escherichia coli. Clone 6D2 was chosen for further study based o n partial nucleotide sequence obtained from p6D2 containing a TnphoA i nsertion. A complete open reading frame (orf1) and a truncated orf (or f2') were identified in the treponemal DNA of p6D2. Orf1 encodes a hyd rophobic protein of 531 amino acids with a calculated M(r) of 57,882 D a. The deduced amino acid sequence of Orf1 has homology to the MglC pr oteins of E. coli, Haemophilus influenzae, and Salmonella typhimurium. T. pallidum Orf1 (MglC) contains a conserved motif that is found in i ntegral cytoplasmic membrane proteins of ATP-binding cassette (ABC) tr ansport systems. T. pallidum ord encodes a protein of 496 amino acids with a calculated M(r) of 55,547 Da. The deduced amino acid sequence o f Orf2 has homology to the MglA proteins of S. typhimurium, E. coli, H . influenzae, and Mycoplasma genitalium. Orf2 (MglA) contains two cons ensus ATP-binding motifs. T. pallidum mglA and mglC are located downst ream of mglB, consistent with the gene order of previously identified mgl operons. The putative T. pallidum mgl operon encodes the first hig h-affinity ABC transport system identified in this spirochete.