The extended promoters for two outer membrane lipoprotein genes of Borrelia spp. uniquely include a T-rich region

OspA and B proteins of Borrelia burgdorferi and Vmp proteins of Borrelia hermsii are abundant outer membrane lipoproteins, whose expression varies with the environment. The genes for these proteins have the '-35' and '-10' elements of a sigma70-type promoter. Deletions of the promoters for these genes were analysed with a chloramphenicol acetyltransferase (CAT) reporter gene and plasmid constructs that were stably maintained in Escherichia coli or transiently transfected into B. burgdorferi. Reporter expression was measured as susceptibility of transformed E. coli cells to chloramphenicol and the CAT activity of E. coli and B. burgdorferi lysates in vitro. Presence of the '-10' element was essential for full activity in both B. burgdorferi and E. coli. Upstream of the '-35' elements of the ospAB and vmp promoters were tracts with Ts in 16 of 20 positions for B. burgdorferi and 18 of 20 positions for B. hermsii. Deletion of the T-rich region from the ospAB or vmp promoter caused a greater reduction of CAT activity in B. burgdorferi than in E. coli. The findings indicate that ospAB and vmp promoters are extended promoters with two parts: (i) a core region containing typical '-35' and '-10' elements and (ii) a unique T-rich region.