Fig 8. A schematic model for regulating intronic tRNAs by the host gene promoter.

tRNA genes are independent entities transcribed by RNA pol III. We showed here that different copies of tRNA are transcribed in a tissue specific manner. One level of regulation can arise from tRNA genes that reside inside intron of a protein coding gene. Shown here are the possible interaction between Pol II gene promoters and Pol III-mediated transcription of intronic tRNAs. Using heat shock promoters we show that promoter repression in cold temperatures can silence the intronic tRNA, and that release of repression in high temperatures enables tRNA expression. The possibility that certain tRNAs can affect the host gene’s expression is also considered (top). Once the gene’s promoter is silenced, tRNA transcription is suppressed (bottom).