A 25-kD inhibitor of actin polymerization is a low molecular mass heat shock protein.
The 25-kD inhibitor of actin polymerization (25-kD IAP), isolated from turkey smooth muscle (Miron, T., M. Wilchek, and B. Geiger, 1988. Eur. J. Biochem. 178:543-553), is shown here to be a low molecular mass heat shock protein (HSP). Direct sequence analysis of the purified protein, as well as cloning and sequencing of the respective cDNA, disclosed a high degree of homology (67% identity, 80% similarity) to the human 27-kD HSP. Southern blot of chicken genomic DNA disclosed one band, suggesting the presence of a single gene, and Northern blot analysis revealed abundant transcript of approximately 1 kb in gizzard and heart tissues and lower amounts in total 18-d chick embryo RNA and in cultured fibroblasts. Exposure of the latter cells to 45 degrees C resulted in over 15-fold increase in the apparent level of the 25-kD IAP protein, confirming that its expression is regulated by heat shock. Immunofluorescent microscopic localization indicated that after heat treatment, the levels of the 25-kD IAP were markedly increased and the protein was apparently associated with cytoplasmic granules. Heat shock also had a transient, yet prominent, effect on the microfilament system in cultured fibroblasts: stress fibers disintegrated within 10-15 min after incubation at 45 degrees C, yet upon further incubation at the elevated temperature, conspicuous actin bundles were apparently reformed.
Miron
T
T
Department of Biophysics, Weizmann Institute of Science, Rehovot, Israel.
Vancompernolle
K
K
Vandekerckhove
J
J
Wilchek
M
M
Geiger
B
B
D008841:Actin Cytoskeleton / Q000187:drug effects / Q000648:ultrastructure; D000199:Actins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D030161:Avian Proteins; D001483:Base Sequence; D015152:Blotting, Northern; D015139:Blotting, Southern; D002478:Cells, Cultured; D002642:Chick Embryo; D003594:Cytoplasmic Granules / Q000378:metabolism / Q000648:ultrastructure; D005347:Fibroblasts / Q000378:metabolism / Q000648:ultrastructure; D005455:Fluorescent Antibody Technique; D006360:Heat-Shock Proteins / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism / Q000494:pharmacology*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009130:Muscle, Smooth / Q000737:chemistry / Q000378:metabolism; D011108:Polymers; D013696:Temperature; D013997:Time Factors; D014422:Turkeys
D000199:Actins; D030161:Avian Proteins; D006360:Heat-Shock Proteins; D011108:Polymers; C069885:actin polymerization inhibitor 25 kDa protein, Meleagris gallopavo