Borrelia burgdorferi supercoiled plasmids encode multicopy tandem open reading frames and a lipoprotein gene family

Stephen F. Porcella, Taissia G. Popova, Darrin R. Akins, Minyue Li, Justin D. Radolf, Michael V. Norgard

Research output: Contribution to journalArticle

77 Scopus citations

Abstract

DNA sequencing and Southern blot analyses of a Borrelia burgdorferi DNA fragment encoding a signal sequence led to the discovery of a genetic locus, designated 2.9, which appears to be present in at least seven copies in virulent B. burgdorferi 297. DNA sequence analysis of these regions revealed that each 2.9 locus contained an operon of four genes (ABCD) and open reading frames designated rep+ (positive strand) and rep-(negative strand) which encoded multiple repeat motifs. Downstream of the rep+ gene(s) in six of the completely cloned and sequenced 2.9 loci also were lipoprotein (LP) genes possessing highly similar signal sequences but encoding variable mature polypeptides. The lipoproteins could be separated into two classes on the basis of hydrophilicity profiles, sequence similarities, and reactivity with specific antibodies. The 2.9 loci were localized to two (20- and 30-kb) supercoiled plasmids in B. burgdorferi 297. Northern (RNA) blot analysis established that the 2.9 ABCD operon was only minimally expressed, whereas the rep- gene(s) and at least three of the seven LP genes were expressed by B. burgdorferi in vitro. A single putative promoter element was identified by RNA primer extension analysis upstream of the ABCD operon, whereas a number of potential promoter regions existed upstream of the LP genes. The combined data indicate that the ABCD operon, rep+ and rep- genes, and LP genes are separately transcribed during in vitro growth. The 2.9 loci possess a repetitiveness, diversity, and complexity not previously described for B. burgdorferi; differential expression of these genes may facilitate the spirochete's ability to survive in diverse host environments.

Original languageEnglish (US)
Pages (from-to)3293-3307
Number of pages15
JournalJournal of bacteriology
Volume178
Issue number11
DOIs
StatePublished - Jun 1996

ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology

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