IDENTIFICATION AND TRANSCRIPTIONAL ANALYSIS OF A TREPONEMA-PALLIDUM OPERON ENCODING A PUTATIVE ABC TRANSPORT-SYSTEM, AN IRON-ACTIVATED REPRESSOR PROTEIN HOMOLOG, AND A GLYCOLYTIC PATHWAY ENZYME HOMOLOG

We have characterized a 5.2-kilobase (kb) putative transport related o peron (tro) locus of Treponema pallidum subsp. pallidum (Nichols strai n) (Tp) encoding six proteins: TroA, TroB, TroC, TroD, TroR and Phosph oglycerate mutase (Pgm). Four of these gene products (TroA-TroD) are h omologous to members of the ATP-Binding Cassette (ABC) superfamily of bacterial transport proteins. TroA (previously identified as Trompl) h as significant sequence similarity to a family of Gram-negative peripl asmic substrate-binding proteins and to a family of streptococcal prot eins that may have dual roles as substrate binding proteins and adhesi ns. TroB is homologous to the ATP-binding protein component, whereas T roC and TroD are related to the hydrophobic membrane protein component s of ABC transport systems. TroR is similar to Gram-positive iron-acti vated repressor proteins (DesR, DtxR, IdeR, and SirR). The last open r eading frame (ORF) of the tro operon encodes a protein that is highly homologous to the glycolytic pathway enzyme, Pgm. Primer extension res ults demonstrated that the tro operon is transcribed from a sigma(70)- type promoter element. Northern analysis and reverse transcriptase-pol ymerase chain reactions provided evidence for the presence of a primar y 1-kb troA transcript and a secondary, less abundant, troA-pgm transc ript. The tro operon is flanked by a Holliday structure DNA helicase h omolog (upstream) and two ORFs representing a purine nucleoside phosph orylase homolog and tpp15, a previously characterized gene encoding a membrane lipoprotein (downstream). The presence of a complex operon co ntaining a putative ABC transport system and a DtxR homolog indicates a possible linkage between transport and gene regulation in Tp. (C) 19 97 Elsevier Science B.V.