Accumulation of stable full-length circular group i intron RNAs during heat-shock
Permanent link
https://hdl.handle.net/10037/10766Date
2016-10-31Type
Journal articleTidsskriftartikkel
Peer reviewed
Author
Andersen, Kasper L.; Beckert, Bertrand; Masquida, Benoît; Johansen, Steinar Daae; Nielsen, HenrikAbstract
Group I introns in nuclear ribosomal RNA of eukaryotic microorganisms are processed
by splicing or circularization. The latter results in formation of full-length circular introns without
ligation of the exons and has been proposed to be active in intron mobility. We applied qRT-PCR
to estimate the copy number of circular intron RNA from the myxomycete
Didymium iridis
.
In exponentially growing amoebae, the circular introns are nuclear and found in 70 copies per
cell. During heat-shock, the circular form is up-regulated to more than 500 copies per cell. The intron
harbours two ribozymes that have the potential to linearize the circle. To understand the structural
features that maintain circle integrity, we performed chemical and enzymatic probing of the splicing
ribozyme combined with molecular modeling to arrive at models of the inactive circular form and
its active linear counterpart. We show that the two forms have the same overall structure but differ
in key parts, including the catalytic core element P7 and the junctions at which reactions take place.
These differences explain the relative stability of the circular species, demonstrate how it is prone to
react with a target molecule for circle integration and thus supports the notion that the circular form
is a biologically significant molecule possibly with a role in intron mobility.