An alteration in molecular form associated with activation of human heat shock factor.
In higher eucaryotes, heat shock factor (HSF) exists in a cryptic form in unstressed cells. We investigated molecular forms of human HSF before and after activation by sucrose density gradient centrifugation and by gel mobility shift assay using a 32P-labeled heat shock element (HSE). We found that the in vivo or in vitro activated HSF, which is capable of binding to HSE, and its inactive form present in unstressed cells have different sedimentation coefficient; the former is 8 S whereas the latter is 4-5 S. Both the 8 S and 4-5 S forms contain the HSF polypeptide which has the ability to bind to HSE upon activation. The inactive 4-5 S form acquires HSE-binding ability when activated by heat shock or other stimuli. This HSF activity was greatly reduced, however, during recentrifugation in sucrose density gradient and, in addition, the residual activity was not recovered in 8 S fractions. Transformation of the inactive 4-5 S form of HSF to the stable, active 8 S form was achieved when the inactive form was activated and mixed with cytosols of unstressed cells.
Department of Cell Biology, Tokyo Metropolitan Institute of Medical Science, Japan.
Y
Y
Kimura
T
T
Taniguchi
I
I
Yahara
D001483:Base Sequence; D002478:Cells, Cultured; D002499:Centrifugation, Density Gradient; D006367:HeLa Cells; D006360:Heat-Shock Proteins / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D006801:Humans; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010761:Phosphorus Radioisotopes
D006360:Heat-Shock Proteins; D010761:Phosphorus Radioisotopes