Silk worm Bm1 SINE RNA increases following cellular insults

The effect of cell stresses upon the expression of the Bm1 short interspers ed element (SINE) family in cultured silk worm cells is examined. Primer ex tension analysis shows that Bm1 repeats are transcribed by RNA polymerase I II (Pol III) into cytoplasmic RNAs. Five consecutive T residues, which woul d normally terminate Pol III transcription, occur within the Bm1 consensus and are included within cDNA sequences representing these transcripts. In a nalogy to mammalian SINEs, the level of the Bm1 transcripts increases in re sponse to either heat shock, inhibiting protein synthesis by cycloheximide or viral infection. The lifetime of Bm1 RNA increases following cell insult s so that post-transcriptional events partially account for stress induced increases in its abundance. In the case of heat shock, the increase in Bm1 RNA follows the transient increase in hsp70 mRNA indicating that this respo nse is temporally regulated to occur later in heat shock recovery. These re sults support the proposal that SINE RNAs serve a role in the cell stress r esponse that predates the divergence of insects and mammals implying that S INEs are essentially a class of cell stress genes.