Part:BBa_K2086001

Serine Repeat Antigen (SerA)

The E. coli serA gene encodes the D-3-phosphoglycerate dehydrogenase, which catalyzes the first committed step in the biosynthesis of serine. Serine is an essential amino acid for E. coli growth in minimal medium. Deletion of the serA gene leads to a serine auxotroph, which can be rescued either by the expression of a protein with the same catalytic activity as SerA or by the addition of serine in the growth media.

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  INCOMPATIBLE WITH RFC[21]

  Illegal BamHI site found at 293
  
• 23
  COMPATIBLE WITH RFC[23]
• 25
  COMPATIBLE WITH RFC[25]
• 1000
  COMPATIBLE WITH RFC[1000]

Biology and Our Application

Figure 1: The serine biosynthesis pathway. Provided by: EcoCyc, a member of the BioCyc database collection http://ecocyc.org/ECOLI/NEW-IMAGE?type=PATHWAY&object=SERSYN-PWY&show-citations=NIL

Serine is an amino acid produced in E. coli K12 through the metabolic pathway shown in Figure 1. The SerA gene codes for D-3-Phosphoglycerate Dehydrogenase, the enzyme responsible for catalyzing the committed step of serine biosynthesis. Without SerA, E. coli are unable to grow without sufficient supplementation of other amino acids [1].

Taking advantage of the bacteria's dependence on serine, we planned to create a safety kill switch by controlling the production of the amino acid. By obtaining an auxotrophic strain missing the SerA strain (JW2880 [2]) we were able to create a complement SerA plasmid to rescue the strain when grown in media without supplementary amino acids.

[1]. PAULA D. RAVNIKAR AND RONALD L. SOMERVILLE: Genetic Characterization of a Highly Efficient Alternate Pathway of Serine Biosynthesis in Escherichia coli. http://jb.asm.org/content/169/6/2611.full.pdf

[2] Coli Generic Stock Center: JW2880. http://cgsc.biology.yale.edu/Strain.php?ID=108515

SerA Supplementation

Our SerA gene was used later in the formation of our composite kill switch: BBa_K2086002

Plasmid Synthesis

Figure 3: The gel electrophoresis results of the two components of our SerA plasmid

After testing, we were able to synthesize a basic SerA ORF plasmid, biobrick compatible with a wide variety of plasmids, promoters, and ribosome binding sites. In Figure 3, you can see the results of our gel electrophoresis, used to ligate the two components of our plasmid:

• pSB1C3 : 2070 bp
• SerA : 1233 bp