both cleaved the UG^C sequence (DIII) (Fig. 4C)
and were sensitive to a U→A mutation (DIV).
Ire1 was still able to cleave the G^C site in
substrate DIV, indicating that the catalytic KEN
protomer of Ire1 provides G^C recognition. To-
gether, our experiments and the studies of RIDD
RNA cleavage (fig. S12).
RNase L is expressed in most human tissues,
which imposes the requirement for a delicate
regulation of this protein to prevent uncontrolled
RNA cleavage, growth inhibition, and apoptosis.
Here, we describe the mechanism of this regu-
lation. Our findings further the understanding of
the IFN response and RIDD and provide a struc-
tural basis for designing synthetic 2-5A analogs
as molecular probes and modulators of IFN
Fig. 3. RNA sequence recognition by RNase L. (A) Structure of RNA bound to the KEN homodimer. Arrows show the RNA trace. RNA cleavage is predicted at
UN^N sites. (B) In trans activation of WT RNase L by the catalytically inactive RNase L mutant H672N. (C) RNase L cleavage of substrates I to VII. (D) RNase L
cleavage of substrates DI and DII.