Heat shock protein (HSP) accumulation and binding to polymerase‐β (Polβ) in the nucleus. H1299 cells were treated at various intervals after a preheating treatment (45.5°C, 5 min). (a) Thermotolerance ratio (TTR). (b) HSP bands in Western blot analysis. Lane 1, untreated control samples. Lanes 2–6, samples at various periods after a heat treatment alone (45.5°C, 5 min): lane 2, 1.5 h; lane 3, 3 h; lane 4, 6 h; lane 5, 12 h; lane 6, 24 h. (c) Density of HSP bands with Western blot analysis. (j) () Hsp27. () Hsp70. (d) Co‐immunoprecipitation experiments with nuclear extracts. Lane 1, non‐heating treatment; lane 2, 3 h after a preheating treatment alone (45.5°C, 5 min); lane 3, challenging heat treatment (45.5°C, 20 min) at 3 h after a preheating treatment (45.5°C, 5 min); lane 4, challenging heat treatment alone (45.5°C, 20 min).