The goals of this new R21 grant are to determine a) how a novel Chlamydia-specific transcription factor designated GrgA controls chlamydial growth by regulating gene expression, and b) whether GrgA is a target for benzylidene acylhydrazides, which have been recognized as novel antichlamydials. Chlamydia is an obligate intracellular bacterium with a unique developmental cycle. It is the most common sexually transmitted bacterial pathogen. Sexually transmitted chlamydial infection often leads to infertility, abortion, ectopic pregnancy and pelvic inflammatory disease. Transcription not only controls chlamydial growth and pathogenicity, but also represents an effective therapeutic target for chlamydial infections. We have identified a highly novel transcription factor that we call GrgA. Encoded by chlamydiae only, GrgA activates transcription in vitro from promoters that require the primary or housekeeping ? factor (a subunit of the RNAP polymerase) designated ?66 by interacting with the non-conserved region of the ? factor. Further evidence support the hypothesis that GrgA plays a critical role in the regulation of chlamydial growth, and is potentially a target for antichlamydials with therapeutic and prophylactic potentials. We propose two Specific Aims to test this hypothesis. In Aim 1, we will identify the regulon of GrgA, and determine how alterations in the GrgA activity affect the transcriptome expression, and growth and developmental properties in Chlamydia. In Aim 2, we will determine the role of GrgA in chlamydial growth inhibition by benzylidene acylhydrazides, a new group of antichlamydials with undetectable toxicity to host cells and beneficial lactobacilli that dominate the vaginal microbiome of healthy, reproductive-age women. We anticipate three significant outcomes from this study: a) this research will yield insights into transcription regulation in chlamydia; b) we may confirm that GrgA is a target of benzylidene acylhydrazides; and c) with an elucidation of the drug targeting mechanism, benzylidene acylhydrazides could prove valuable as chemical probes for studying chlamydial biology.