During its developmental

cycle, there is conversion between two distinct morphological forms, the elementary bodies (EBs) and reticulate bodies (RBs) [12, 13]. The EBs are the infectious form and upon entry into a host cell, they differentiate into metabolically active reticulate bodies (RBs), which are larger compared to EBs and divide by binary fission [12–14]. The reticulate bodies are also non-infectious forms [14]. Later in the developmental cycle, RBs convert back to EBs, which are released from infected cells [12, 14]. The transformation of RBs to EBs by E. chaffeensis is observed in both vertebrate and tick hosts [15]. The mechanism by which the pathogen survives in dual hosts Lapatinib by adapting to changes in different host environments is unclear. Recent studies described the differential gene and protein expression profiles of the

pathogen originating from tick and mammalian cell environments [15–18]. Moreover, E. chaffeensis organisms recovered from infected tick cells produce longer-lasting infections in mice compared to the infection with organisms harvested from mammalian macrophages Gefitinib [19]. Differentially expressed proteins of E. chaffeensis included the predominant expression from outer membrane protein genes p28-Omp19 and p28-Omp14 in mammalian and tick cell environments, respectively [15–19]. The adaptive response to different host environments requires altering the gene expression, often regulated at the transcriptional level by altering RNA polymerase (RNAP) activity [20]. A typical bacterial RNAP consists of five polypeptide chains; two α subunits, one each of β and β’ subunits, and a σ subunit. The enzyme can take two forms, a holoenzyme containing all four different subunits or core polymerase that lacks a σ Urease subunit [21]. The capacity to synthesize RNA resides in the core polymerase and the role of a σ subunit is to direct initiation of transcription from specific promoters [22, 23]. The genome of E. chaffeensis includes two sigma factor genes; the homologs of the major bacterial sigma factor, σ70, and an alternative sigma factor, σ32 [24]. The current lack of established methods to stably transform, transfect, conjugate, or electroporate E.

chaffeensis remain a major limiting factor to study mechanisms of gene expression by traditional methods. Mapping the functions of E. chaffeensis genes in vivo cannot be performed because genetic manipulation systems are yet to be established. To overcome this limitation, in a recent study we reported the utility of Escherichia coli RNAP as a surrogate enzyme to characterize E. chaffeensis gene promoters [25]. Although the E. coli RNAP proved valuable for mapping E. chaffeensis gene promoters, the extrapolation of the data requires further validation using the E. chaffeensis RNAP. In this study, we developed a functional in vitro transcription system by utilizing G-less transcription templates [26] to drive transcription from two E. chaffeensis promoters.