Chlamydia trachomatis protein GrgA activates transcription by contacting the nonconserved region of σ ⁶⁶

Abstract

The bacterial RNA polymerase holoenzyme consists of a catalytic core enzyme in complex with a σ factor that is required for promoter-specific transcription initiation. Primary, or housekeeping, σ factors are responsible for most of the gene expression that occurs during the exponential phase of growth. Primary σ factors share four regions of conserved sequence, regions 1-4, which have been further subdivided. Many primary σ factors also contain a nonconserved region (NCR) located between subregions 1.2 and 2.1, which can vary widely in length. Interactions between the NCR of the primary σ factor of Escherichia coli, σ 70 , and the β′ subunit of the E. coli core enzyme have been shown to influence gene expression, suggesting that the NCR of primary σ factors represents a potential target for transcription regulation. Here, we report the identification and characterization of a previously undocumented Chlamydia trachomatis transcription factor, designated GrgA (general regulator of genes A). We demonstrate in vitro that GrgA is a DNA-binding protein that can stimulate transcription from a range of σ 66 -dependent promoters. We further show that GrgA activates transcription by contacting the NCR of the primary σ factor of C. trachomatis, σ 66 . Our findings suggest GrgA serves as an important regulator of σ 66 -dependent transcription in C. trachomatis. Furthermore, because GrgA is present only in chlamydiae, our findings highlight how nonconserved regions of the bacterial RNA polymerase can be targets of regulatory factors that are unique to particular organisms.

Structural, functional, and genetic analyses of the actinobacterial transcription factor RbpA

“…1C, 2 A-C, and S1). Interacting with the primary σ-NCR is a property that RbpA shares with the unrelated Chlamydia trachomatis transcription factor GrgA, which binds to the Chlamydia trachomatis σ 66 -NCR (20). Moreover, although structurally distinct from RbpA, the holoenzyme assembly factor Crl from enteric bacteria interacts with the equivalent region of the group 2 σ-factor σ S (21,22).…”

Chlamydia trachomatis Plasmid-Encoded Pgp4 Is a Transcriptional Regulator of Virulence-Associated Genes

“…It is possible that Pgp4-DNA interactions require additional protein partners for successful DNA binding to occur. Of note, it has recently been reported that efficient transcription activation of several promoters by a chlamydial specific transcription factor, general regulator of genes A (GrgA), in vitro requires contact with both DNA and a portion of a nonconserved region of the primary factor, 66 , of C. trachomatis (53). Studies are under way to determine the molecular mechanism of Pgp4-mediated gene regulation.…”

Regulation of Chlamydia Gene Expression by Tandem Promoters with Different Temporal Patterns

“…This strategy allows a chlamydial gene to be controlled by multiple regulatory signals and to have a hybrid temporal expression pattern that may not be possible with a single promoter. Chlamydia has a limited means to differentially regulate its genes because it has only about a dozen transcription factors (6,19,(22)(23)(24). Tandem promoters provide a relatively simple approach to fine-tune the expression of a chlamydial gene by using existing mechanisms of temporal regula-…”