SINE RNAs control the heat shock response in mouse and human cells. A) Pol III transcribed SINE RNAs increase upon heat shock. B) During heat shock, mouse B2 RNA or human Alu RNA enters complexes at the promoters of repressed genes. TFIIF facilitates dissociation of B1 RNA from Pol II. C) Heat shock activated genes are resistant to repression by B2 RNA and Alu RNA.