Abstract: Based on morphologically comparative studies on amicronucleates and micronucleates of a ciliate protozoa,Pseudourostyla cristata, it is supposed that the micronucleus absence may result in abnormal development of the subsurface cytoskeleton and/or other supportive elements in the vicinity of the AZM during depression phase such as starvation.To understand the molecular events governing this mode, we employed suppression subtractive hybridization(SSH)to identify candidate genes which express in micronucleate cells but not in amicronucleate specimens during starvation.A total of 284 transcripts were screened by cDNA array.17 clones were confirmed to be differentially expressed among micronucleate cells.The ESTs(expressed sequence tags)were analyzed by blaster matching in GeneBank at nucleotide and deduced amino acid sequence:11 clones showing no homolgous protein;4 clones showing myoglobin protein;1 clone showing, cytosolic malate dehydrogenase.Interestingly, the last clone, homolog of hsp90.Traditionally, heat shock proteins are known for their function during cellular stress as molecular chaperones responsible for the folding, refolding and transport of newly synthesized protein.As to whether Hsp90 homolog is associated with microtubules in AZM to hold up its structure, and why it is significantly enhanced in micronucleate cells during starvation, further research need to be carried out.