Regulation of sacX expression by SacY and NusG
Open Access
- Author:
- Wein, Tejas
- Area of Honors:
- Biochemistry and Molecular Biology
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Paul Babitzke, Thesis Supervisor
Lorraine C Santy, Thesis Honors Advisor - Keywords:
- bacillus subtilis
NusG
transcription
rna polymerase
pausing
antitermination
microbiology
sacx
sacy
sact
babitzke - Abstract:
- Transcription in Bacillus subtilis is regulated at the levels of initiation, elongation, and termination. During elongation, the activity of RNA polymerase is modified by pausing events stimulated by signals in the template or nascent transcript, protein factors such as NusG, or a combination of both. In antitermination regulatory mechanisms, formation of secondary structures in the 5’ untranslated region of the nascent RNA transcript promotes continued transcription elongation and readthrough; these structures are often stabilized by factors that promote gene expression. The sacX gene is involved in sucrose metabolism. The 5’ untranslated region of sacX contains a ribonucleic antiterminator (RAT) that is stabilized by SacY or SacT in the presence of sucrose growth conditions. In the absence of sucrose, SacY or SacT do not bind to the RNA, the RAT is not stabilized, and an intrinsic termination hairpin forms such that transcription terminates in the 5’ untranslated region. The sacX leader also contains a TTNTTT motif characteristic of NusG-mediated pausing. In sucrose growth conditions, pausing is thought to allow more time for binding of SacY and SacT that promote transcript readthrough and gene expression. Without NusG or the sequence elements needed to promote pausing, there is insufficient time for regulatory factor binding even in sucrose growth conditions, preventing transcript readthrough and gene expression. This expression pattern was confirmed in vivo using sacX-lacZ transcriptional fusions. Additionally, in vitro transcription assays confirmed the presence of a strong NusG-dependent pause site that depends on the TTNTTT sequence motif in the sacX leader.