Gonococcal genes encoding transferrin-binding proteins A and B are arranged in a bicistronic operon but are subject to differential expression

Infect Immun. 2001 Oct;69(10):6336-47. doi: 10.1128/IAI.69.10.6336-6347.2001.

Abstract

Neisseria gonorrhoeae is capable of utilizing host iron-binding proteins, such as transferrin, lactoferrin, and hemoglobin, as the sole source of iron. The receptor involved in transferrin iron acquisition is composed of two distinct transferrin-binding proteins, TbpA and TbpB. The genes that encode these proteins are linked on the chromosome in the order tbpB-tbpA but are separated by an inverted repeat of unknown function. In this study, we sought to understand the transcriptional organization and regulation of the tbp genes, using a combination of lacZ transcriptional fusion analysis and reverse transcriptase PCR (RT-PCR). First, we demonstrated that tbpB and tbpA are cotranscribed and coregulated from the common upstream promoter that precedes tbpB. Using beta-galactosidase activity as a surrogate for tbp-specific transcription, we found that tbpB-specific transcripts were more prevalent than tbpA-specific transcripts after 2 h of growth under iron stress conditions. We confirmed the results obtained by fusion analysis by using RT-PCR applied to native RNA isolated from wild-type gonococci. Three different varieties of RT-PCR were employed: relative, competitive, and real time quantitative. The results of all analyses indicated that tbpB-specific transcripts were approximately twofold more prevalent than tbpA-specific transcripts at steady state. In iron-stressed cultures, the ratio of tbpB- to tbpA-specific message was approximately 2; however, in iron-replete cultures, this ratio dropped to 1. Using these techniques, we also quantitated the effects of iron, external pH, and presence of ligand on tbp mRNA levels.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Artificial Gene Fusion
  • Carrier Proteins / genetics*
  • Culture Media
  • Gene Expression*
  • Hydrogen-Ion Concentration
  • Iron
  • Iron-Binding Proteins
  • Lac Operon
  • Ligands
  • Neisseria gonorrhoeae / genetics*
  • Neisseria gonorrhoeae / growth & development
  • Operon*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Time Factors
  • Transcription, Genetic
  • Transferrin-Binding Proteins

Substances

  • Carrier Proteins
  • Culture Media
  • Iron-Binding Proteins
  • Ligands
  • Transferrin-Binding Proteins
  • Iron