Odd problem with sequencing gels

[Brian Foley]

The doctor is IN. (aarment at desire.wright.edu) wrote:
: 	I am having an odd problem with my sequencing gels that no one around
: the university can offer an explanation for; thus, I appeal to the wisdom of
: the bionet.  My problem is this... when I run a sequencing gel, everything
: begins just fine.  I like to run around 1700V and 40W.  The gel preheats, I
: load it, and then trouble begins.  Over the course of the run, the wattage
: begins to decline (and with it the ampage), although the voltage remains
: constant.  After about two hours, the wattage is down to 25W, and the gel has
: cooled to the point where it is useless for sequencing.
: 	I have changed gel buffer systems (TBE and TEB), changed the way I pout
: my gels, changed the percantages of acrylamide, recirculated the buffer,
: and completely changed the buffer; all to no avail.  The power
: supply appears to be working correctly.  It runs other gel boxes without this
: porblem.  I can generate current across the upper well but NOT through the gel.
: Does anyone have any ideas and/or suggestions as to what is going on?

: Anthony Arment
: Wright State University 

	Are you SURE that your power supply is set up to supply constant
power (watts) and not set up to supply a constant voltage?
	To me, it looks like you have it set to supply a constant 1700
volts.  As the resistance goes up due to heat and other factors durring
the run the 1700 volts no longer provides the same wattage across the
gel.
	I run my gels at 65 watts constant power, the voltage starts out
at about 1700 volts and increases to nearly 2300 volts by the end of the
run.

--
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*  Brian Foley               *     If we knew what we were doing   *
*  Molecular Genetics Dept.  *     it wouldn't be called research  *
*  University of Vermont     *                                     *
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