McClean: Fixation of Yeast (Bisaria Protocol)
This is the protocol used by Anjali Bisaria for rapidly fixing yeast cells from chemostat cultures to image for both bud index as well as fluorescence. We found that protocol preserved both GFP and mCherry fluorescence well.
- Yeast cells
- Formaldehyde 37% (Sigma-Aldrich, #252549)
Add approximately 0.6μL of cells (tiny amount) with the tip of a sterile toothpick into the bottom of PCR tubes or plate. Once you've put cells into the PCR vessel, put the end of the toothpick into ~100μL sterile YPD in either an eppendorf or the well of a culture plate. You will use this to inoculate an overnight culture if your colony PCR works. Keep the eppendorfs or culture plate at either room temperature or 30°C while you run the PCR, either is fine.
Microwave cells in the PCR tube/plate for 1min (2X). Put microwaved cells on ice.
Add the reaction mix (described below) to the PCR tube/plate. It is recommended to make up a master mix if you are doing multiple colonies. Put the PCR tubes/plate into the thermocycler and run the Colony PCR program described below.
PCR Reaction Mix
|10x HotMaster Taq Buffer with Mg2+||5μL|
|10mM dNTP mix||1μL|
|10μM Primer 1||1μL|
|10μM Primer 2||1μL|
|HotMaster Taq DNA polymerase||0.5μL|
Run PCR on Colony PCR program :
- 95°C 4min
- For the following steps, reduce the temperature ‐1°C each cycle and cycle 30x's
- 94°C 1min
- 65°C 1min
- 68°C 2min
- For the following steps, cycle 30x's
- 94°C 30sec
- 50°C 30sec
- 72°C 1min
- 72°C 5min
- 4°C Forever
- Please don't leave the thermocycler running at 4°C for longer than an hour or so, it wears out the machine. If you need to leave your PCR for longer, please change the last step of the program so that instead of holding at 4°C the program just ends (letting the samples come to room temperature). Letting the sample come to room temperature, even overnight, does not seem to cause any problems for the DNA.
'Freezing Down Positive Transformants'
Once you have run the colony PCR and confirmed which colonies are correct and which are not, take the 100μL of YPD that you set aside before, inoculate it into 4mls of fresh YPD in a test tube, and grow it to saturation overnight. Use this to freeze down glycerol stocks of the strain the following morning.
Please feel free to post comments, questions, or improvements to this protocol. Please sign your name to your note by adding '''*~~~~''': to the beginning of your tip.
*Megan N McClean The lengthy touchdown PCR program protocol was devised by Megan in the early days of the McClean lab when we were struggling with getting colony PCR to work reproducibly. The program is probably WAY longer and more complicated than it needs to be (and ties up the thermocycler for 4 hours at a time) so it would be worth someone's time to figure out a shorter program. Once you do that, please add it as another colony PCR protocol on openwetware and add a note here.
*Megan N McClean We probaby don't need to be using the Hotmaster Taq nor do we need to be doing 50μL reactions. If someone has some spare time, please try optimizing the protocol to use our super-cheapy Taq (ask Megan for where the stock is) and doing smaller reaction volumes.
Botstein Lab protocols: http://www.princeton.edu/genomics/botstein/protocols/colony_PCR.htm
or instead, discuss this protocol.