A conserved, transcriptionally active p28 multigene locus of Ehrlichia canis

Antigenic diversity of Ehrlichia chaffeensis and Ehrlichia canis may involv e independent or differential expression of the P28 outer membrane proteins genes, enabling persistent infections of the natural hosts. In this study, we analyzed the transcriptional activity of a five gene locus in E. canis encoding homologous, but non-identical, p28 genes. The p28 multigene locus contained three previously identified complete gene sequences and one parti al gene sequence. A new p28 gene was identified and sequenced, and the comp lete sequence of a second partial p28 gene was determined. The new p28 gene joined two previously separate loci, forming: the single p28 multigene loc us. The amino acid homology of the E. canis P28 proteins ranged from 51 to 74%. The nucleic acid sequence of regions compared within the locus spannin g four p28 genes from two geographically distinct E. canis isolates was com pletely conserved. Analysis of the five p28 genes demonstrated that all wer e transcriptionally active in in-vitro cultures of E, canis incubated at th e vertebrate host (37 degrees C) and ambient tick temperatures (27 degrees C). Polycistronic copies of multiple p28 genes were not detected by RT-PCR, but monocistronic p28 mRNA transcripts were detected by Northern blotting from E. canis infected DH82 cells, indicating that the genes are transcribe d as monocistronic messages. (C) 2000 Elsevier Science B.V. All rights rese rved.