Simply Cloning – Supplement 2 – Cracking Gel


But what if you do have colonies on Vector
plus Insert plate, but they don’t carry the clones that you want? For example, you have 16 colonies on Vector
plus Insert and 12 colonies on the control. You miniprepped and tested a few of them but
did not find the right construct. With the cracking gel you can screen several
dozen colonies in less than an hour and know if any of them has a desired clone. Here is the protocol for making a cracking
buffer and for the cracking gel procedure. Cracking buffer:
* 39.5 ml ddH2O * 2.5 ml 1M NaOH
* 2.5 ml 10% SDS * 0.5 ml 0.5M EDTA Cracking gel protocol:
* Add 20 µl of ddH2O to a tube * Transfer an E. coli colony with a pipette
tip * Add 20 µl of cracking buffer
* Add 20 µl of loading dye * Run on an 0.7% agarose gel Right here on the bench I have a plate with
18 colonies that I am going to screen by a cracking gel. I also have a replica plate, a tube with the
cracking buffer, 18 new Eppendorf tubes, double distilled water, gel loading dye with bromophenol
blue, and a tube with a miniprep of parental plasmid, in this case pSAT6-MCS, that will
serve as a control. Let’s move on to the cracking gel protocol
itself. I start by adding to each of the tubes 20
µl of water. In the tube one, which will serve as a control,
I will put 1 µl of parental plasmid, pSAT6-MCS. In the rest of the tubes I will transfer the
colonies by picking them with pipette tips, dipping the tips in the tubes with 20 µl
of water, and leaving them in the tubes for the moment. Once all the tips are in their tubes, I am
going to shake off the cells by vortexing the tubes at low speed with the tips inside. Then I take every tip and touch the labelled
LB replica plate. I will keep this plate at 37oC overnight. Once all the cells are in, I am going to lyse
them by adding 20 µl of the cracking buffer to each of the tubes. Notice that there is
no mixing involved at this step. I immediately proceed with adding 20 µl of
loading dye with bromophenol blue and glycerol. I load contents of each of the tubes on a 0.7%
agarose gel and run it for 1 hour at 105 volts. Notice that for the cracking gel I am using
the 0.7% agarose, which allows for better separation of large DNA fragments. Let’s look at the picture of this gel. Since
we run whole cell lysates here, we can see three types of nucleic acids: RNA is that
big smear at the bottom, at the very top is genomic DNA, and the plasmid we are looking
for is in the middle. In the control lane you see how the vector
would run if it did not have an insert. Out of the 18 colonies that we are screening
here, only plasmids from colonies 6 and 14 run higher than the control, which means they
should have the insert we were trying to introduce. On the next day we can go back to the replica
plate, and start the miniprep cultures with clones 6 and 14.

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