In vivo coupling between groupIIC intron insertion and transcriptional termination

Abstract

Group II introns are a class of retroelements consisting of a catalytic RNA and an intron-encoded protein (IEP), which is a reverse transcriptase (RT). Group II ribozymes are classified into three subgroups, IIA, IIB and IIC. IIC introns have the novel mobility property of inserting directly after transcriptional terminator motifs rather than into homing sites of defined sequence. This dissertation addresses a direct correlation between intron homing and terminator motifs by using a set of in vivo experiments. Target DNAs were constructed such that the native terminator motif was replaced with sequences from the E. coli tryptophan attenuator or the B. subtilis adenine, SAM, FMN or lysine riboswitches. The data support a model for in vivo mobility in which the intron’s RNP (intron lariat bound by IEP) gains access to its unwound DNA target during the pause of transcriptional termination, allowing it to recognize the DNA stem-loop structure.