Analysis of Transcriptionally Active Gene Clusters of Major Outer Membrane Protein Multigene Family inEhrlichia canisandE. chaffeensis

• DOI: 10.1128/iai.69.4.2083-2091.2001
• Publication Date: 2002-07-27T09:58:18Z
• Authors: Norio Ohashi; Yasuko Rikihisa; Ahmet Unver
• Keywords: Ehrlichia chaffeensis; Transcription, Genetic; Multigene Family; Ehrlichia; Chromosome Mapping; Cloning, Molecular; Bacterial Outer Membrane Proteins; Repetitive Sequences, Nucleic Acid

ABSTRACTEhrlichia canisandE. chaffeensisare tick-borne obligatory intramonocytic ehrlichiae that cause febrile systemic illness in humans and dogs, respectively. The current study analyzed the pleomorphic multigene family encoding approximately 30-kDa major outer membrane proteins (OMPs) ofE. canisandE. chaffeensis. Upstream fromsecAand downstream of hypothetical transcriptional regulator, 22 paralogs of theompgene family were found to be tandemly arranged except for one or two genes with opposite orientations in a 28- and a 27-kb locus in theE. canisandE. chaffeensisgenomes, respectively. Each locus consisted of three highly repetitive regions with four nonrepetitive intervening regions.E. canis, in addition, had a 6.9-kb locus which contained a repeat of three tandem paralogs in the 28-kb locus. These total 47 paralogous and orthologous genes encoded OMPs of approximately 30 to 35 kDa consisting of several hypervariable regions alternating with conserved regions. In the 5′-end half of the 27-kb locus or the 28-kb locus of eachEhrlichiaspecies, 14 paralogs were linked by short intergenic spaces ranging from −8 bp (overlapped) to 27 bp, and 8 remaining paralogs in the 3′-end half were connected by longer intergenic spaces ranging from 213 to 632 bp. All 22 paralogs, five unknown genes, andsecAin theompcluster inE. caniswere transcriptionally active in the monocyte culture, and the paralogs with short intergenic spaces were cotranscribed with their adjacent genes, including the respective intergenic spaces at both the 5′ and the 3′ sides. Althoughompgenes are diverse, our results suggest that the gene organization of the clusters and the gene locus are conserved between two species ofEhrlichiato maintain a unique transcriptional mechanism for adaptation to environmental changes common to them.