I worked in the medical library at a hosptial. I found the information in books on CJD - Crutzfedlt Jacobs Disease, caused by folded proteins. Two doctors at the hospital had been in England the previous year and verified that, to their knowledge, the information was correct.
Here's the section of the Wikipedia article on prions regarding "Sterilization":
"Infectious particles possessing nucleic acid are dependent upon it to direct their continued replication. Prions however, are infectious by their effect on normal versions of the protein. Therefore, sterilizing prions involves the denaturation of the protein to a state where the molecule is no longer able to induce the abnormal folding of normal proteins. However, prions are generally quite resistant to denaturation by proteases, heat, radiation, and formalin treatments,[31] although their infectivity can be reduced by such treatments.
"Prions can be denatured by subjecting them to a temperatures of 134 degrees Celsius (274 degrees Fahrenheit) for 18 minutes in a pressurised steam autoclave.[32] Ozone sterilization is currently being studied as a potential method for prion deactivation.[33] Renaturation of a completely denatured prion to infectious status has not yet been achieved, however partially denatured prions can be renatured to an infective status under certain artificial conditions.[34]
Note that "resistant to" is not the same as "impervious to" various sterilant agents.
Also note that 134 degrees Centigrade is not a particularly high temperature in chemistry, though it may be considered so in hospital sterilization.
So I say again--a sufficiently high temperature WILL denature the "prionic proteins", rendering them non-infectious.
And in fact, I recall one article from Britain saying that no evidence of prion-transmitted diseases among cattle were observed UNTIL the relevant regulatory department in charge of rendering plants LOWERED the recommended cooking temperature and time. With the higher temperature, there had been no problem.