Search for: [Abstract = "A plethora of heat shock transcription factors \(HSFs\) has been obtainedfrom various plant species \(33,45\-48,50,51\). The Arabidopsis genome sequencingproject provided confirmation of the existence of at least twenty one HSFswhich were classified into three major classes. A, B and C, and numerous subclasses \(9\). Members of HSF class A displayed differential transcriptional activities in tobacco protoplasts that varied from 15\- to 50\-fold above the controllevel. This diversity of activity levels may reflect HSF variations regarding theirtranscriptional activation functions\- some of the members might be the majorheat inducible HSFs \(class A1 HSFs\), while others act in an auxiliary capacity asHSF activity boosters \(38\). Two new class B HSFs showed no transcriptional activation potential. Reporter activities due to endogenous tobacco HSFs were inhibited by a class B HSFs showing high expression levels. This suppression ofendogenous HSFs by class B members provides further evidence that class BHSFs are not transcriptional activators, but are able to trons\-attenuate thetranscriptional activity of bona fide activator HSFs \(34,41\). The transcriptionalcompetency of class C HSFs has not been determined."]

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