Part:BBa_K1379004

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., () 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

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  COMPATIBLE WITH RFC[25]
• 1000
  INCOMPATIBLE WITH RFC[1000]

  Illegal BsaI site found at 298
  

Reference

BioCyc: http://www.biocyc.org/SPNE171101/NEW-IMAGE?type=GENE&object=GJC8-2079 Luo, P., & Morrison, D. A. (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