Major outer membrane proteins of Ehrlichia ruminantium encoded by a multigene family

Immune responses of infected animals and humans have been reported to be directed against variable outer membrane proteins of Ehrlichia species that are encoded by polymorphic multigene families. In Ehrlichia (= Cowdria) ruminantium, two immunodominant proteins have been identified, namely major antigenic protein 1 (MAP1) and open reading frame 2 (ORF2). The aim of the present study was to identify additional map1-like genes in the E. ruminantium genome. A 12 kb clone that hybridized with the map1 probe was amplified using long template PCR. The PCR product was partially digested, cloned, and sequenced. Four map1-like genes are located in tandem, namely map1-1 (orf2) and map1-2 upstream of map1 as well as map1+1 downstream of map1. A large ORF (2.4 kb) at the 3' end is homologous to secA genes of other organisms. The sequence data in this study support other findings that outer membrane proteins are located in tandem and are encoded by a polymorphic multigene family.