text: <unk> s <unk>  are a group of proteins whose expression is increased when the cells are exposed to elevated temperatures or other stress.  This increase in expression is transcriptionally regulated.  This dramatic upregulation of the<unk> s induced mostly by<unk><unk>  Factor (HSF) is a key part of the<unk><unk>  response.
  The<unk> s are named according to their molecular weights. For example,<unk> 60,<unk> 70 and<unk> 90 (the most widely-studied<unk> s) refer to families of<unk> s on the order of 60, 70 and 90 kilodaltons in size, respectively. The small 8 kilodalton protein ubiquitin, which marks proteins for degradation, also has features of a<unk> .
  The function of<unk> s is similar in virtually all living organisms, from bacteria to humans. The major classes of<unk> s are tabulated below.
option_0: Heat shock protein
option_1: Extractable nuclear antigens
option_2: Cycasin
option_3: Ribosomal RNA
option_4: Sarcomere
option_5: Acute phase protein
option_6: Viral envelope
option_7: Motor protein