Difference between revisions of "Part:BBa K1379004"

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S. pneumoniae σ^x CDS

Usage and Biology

σ^X (ComX) is an alternative σ factor in Streptococcus pneumoniae which serve as a competence-specific global transcription modulator. (BioCyc) In S. pneumoniae, competence (a state capable of being genetic transformed) happens transiently during the log phase growth, and is regulated by a quorum sensing system utilizing the Competence Signal Peptide (CSP). (Luo & Morrison, 2003) Upon stimulation by CSP, σ^X will be expressed and associate with RNA polymerase apoenzyme. The resulting holoenzyme will then be guided by σ^X to initiate transcription of a set of “late” genes enabling genetic transformation and other unknown functions. (Piotrowski, Luo, & Morrison, 2009)

iGEM 2014 Hong_Kong_HKUST Team has cloned σ^X from S. pneumoniae strain NCTC7465 and characterized its ability to initiate transcription of two downstream promoters: P_chbB(BBa_K1379000) and P_comFA (BBa_K1379001).

Following the principle depicted in Rhodius et al., (Rhodius et al., 2013) σ^X could achieve orthogonal gene expression regulation if used together with other sigma factors / ECFs. It should be noted that iGEM 2014 Hong_Kong_HKUST Team has compared the amino acid sequences of ECFs described by Rhodius et al. with that of σ^X from S. pneumoniae, and found no significant similarities, thus σ^X is a new sigma factor added to the list.

Characterization

To test the functionality of σ^X, we first enabled constitutive expression of σ^X in the σ^X Generator BBa_K1379006. The generator was then assembled with the promoter measurement kit BBa_E0240 with either promoter P_chbB (Promoter only: BBa_K1379000, w/ BBa_E0240: BBa_K1379002) and P_comFA (Promoter only: BBa_K1379001, w/ BBa_E0240: BBa_K1379003). E. coli colonies holding the resulting constructs in pSB3K3 were observed under fluorescent macroscope with UV filter. Measurement kit for standard reference promoter BBa_J23101, BBa_I20260 was used as a positive control; BBa_E0240 was used as the general negative control. for background fluorescence. Measurement kits for P_chbB P_comFA without σ^X Generator were used as negative controls for function of σ^X.

As shown below, only in the presence of σ^X would P_chbB and P_comFA be turned on, therefore, σ^X is functional.

Figure 1. P_chbB and P_comFA promoters activated in presence of σ^X. P_chbB and P_comFA gave little GFP signal in the absence of σ^X but has comparable activity as reference promoter BBa_J23101 in presence of σ^X. Scale bar = 5mm.

Extensive documentation of our characterization can be found at our [http://2014.igem.org/Team:Hong_Kong_HKUST/pneumosensor/characterization characterization page for Pneumosensor].
Please refer to the pages BBa_K1379000 (P_chbB) and BBa_K1379001 (P_comFA) for detailed characterization on the promoter activities in presence of σ^X.

Sequence and Features

Reference

BioCyc was retrieved from http://www.biocyc.org/SPNE171101/NEW-IMAGE?type=GENE&object=GJC8-2079
Luo Ping, & Morrison Donald. (2003). Transient Association of an Alternative Sigma Factor, ComX, with RNA Polymerase during the Period of Competence for Genetic Transformation in Streptococcus pneumoniae. Journal of Bacteriology. doi:10.1128/JB.185.1.349-358.2003
Piotrowski Andrew, Luo Ping, & Morrison Donald. (2009). Competence for genetic transformation in Streptococcus pneumoniae: termination of activity of the alternative sigma factor ComX is independent of proteolysis of ComX and ComW. Journal of Bacteriology. doi:10.1128/JB.01750-08
Rhodius Virgil., Segall-Shapiro Thomas., Sharon Brian., Ghodasara Amar., Orlova Ekaterina., Tabakh Hannah., . . . Voigt Christopher. (2013). Design of orthogonal genetic switches based on a crosstalk map of σs, anti-σs, and promoters. Molecular Systhetic Biology .doi:10.1038/msb.2013.58