Difference between revisions of "Part:BBa K3570008"

Revision as of 17:51, 27 October 2020

HIS3 selection marker

Usage

HIS3 gene, found in the Saccharomyces cerevisiae yeast, encodes a protein called Imidazoleglycerol-phosphate dehydratase which catalyzes the sixth step in histidine biosynthesis(1). It is analogous to hisB in Escherichia coli.

HIS3 gene serves as a commonly used yeast selectable marker. When HIS3 gene is inserted into an integrative or replicative plasmid, HIS3 allows to counter-select the cells that acquired the prototroph character for histidine so that they can grow without histidine addition in the medium. Those cells should not have the functional HIS3 gene in its genome[1].

The sequence contains HIS3 specific promoter, HIS3 coding sequence, and HIS3 terminator. This sequence was taken from RS313 plasmid [3].

Experiments

We used this part to selection transformed colonies with the part BBa_K3570000 (coding for tHMG1 and CrtE). Below is our yeast transformation protocol and our results which show that the BBa_K3570008 works.

A. Protocols

Fresh yeast were grown in 25ml of YPD medium overnight. This preculture was diluted to low OD_600nm (e.g. 0.05) in 50ml of fresh YPD medium. The biomass concentration was measured every two hours until it reaches an OD_600nm of around 0.8. The 50ml of culture was transfered in a 50ml falcon-tube and was centrifuged 5 minutes at 3000rpm at room temperature. The supernatant was removed and 25ml of LiAc/TE was added. The tube had to be thoroughly inverting 10 times. The tube was centrifuged 5 minutes at 3000rpm at room temperature. The supernatant was removed and 400µl of LiAc/TE was added. The tube had to be thoroughly inverting 10 times. Yeast competent cells should be used on the same day that they have been prepared.

A mix in 1.5ml microcentrifuge tube was prepared with 2µl of transforming DNA (BBa_K3570000), 40µl of competente yeast cells , 25µg of carrier DNA (SS-DNA) and 168µl of 50% PEG in 100mM LiAc/TE. Positive control was the same mixture but the transforming DNA was replaced by 1uL of pR313 (a plasmid which have the HIS3 marker). The negative control was the same mixture but had no transforming DNA. After vortexing, the solution was incubated 45 minutes at 30°C. Then 13µl of DMS0 was added and the solution was vortexed again. It was centrifuged at 10,000 rpm for 1 minute. The supernatant was removed and the pellet was resuspended in 80µl of NaCl. The solution was seeded on petri dishe of YNB with all amino acids expect histidine. The petri dishe was incubated at 30°C for three days.

B. Results and discussion

The strain BY4741 Saccharomyces cerevisiae was transformed and was grown on YNB with all amino acids expect histidine for 3 days. We were able to observe around 20 colonies in our yeast transformation, about the same on the positive control and none on the negative control plate. This result prove that the HIS3 selectable marker works.

References

• [1]- Old, R. W., & Primrose, S. B. (1981). Principles of gene manipulation: an introduction to genetic engineering (Vol. 2). Univ of California Press.
• [2]- GenBank: U03439.1
• [3]- RS313 plasmid
• [4]- SGD:S000005728

Sequence and Features