RNA at the steering wheel

Abstract

Expression of the genetic information encoded in our genomes is usually regulated by proteins interacting with the DNA. In some cases, however, noncoding RNAs transcribed from DNA control elements cooperate with histone-modifying enzymes to regulate gene expression, as has recently been shown for noncoding RNA originating from Polycomb- and Trithorax-group response elements.

Figure 1

RNA polymerase II (Pol II) transcription through the bxd PRE/TRE leads to the generation of noncoding tre1, tre2 and tre3 RNAs. These RNAs remain tethered to their site of origin, presumably via base pairing with the unwound single-stranded DNA. The histone methyltransferase ASH1 specifically interacts with tre1, tre2 and tre3 RNAs and thus becomes targeted to the PRE/TRE. Through its SET domain, ASH1 catalyzes the trimethylation (Me) of lysines 4 and 9 on histone H3, and of lysine 20 on histone H4. This leads to the activation of the chromatin structure and, as a consequence, the stimulation of Ubx expression.