2 research outputs found
Structural and Mechanistic Insights into Poly(uridine) Tract Recognition by the hnRNP C RNA Recognition Motif
HnRNP C is a ubiquitous RNA regulatory
factor and the principal
constituent of the nuclear hnRNP core particle. The protein contains
one amino-terminal RNA recognition motif (RRM) known to bind uridine
(U)-rich sequences. This work provides a molecular and mechanistic
understanding of this interaction. We solved the solution structures
of the RRM in complex with poly(U) oligomers of five and seven nucleotides.
The five binding pockets of RRM recognize uridines with an unusual
5′-to-3′ gradient of base selectivity. The target recognition
is therefore strongly sensitive to base clustering, explaining the
preference for contiguous uridine tracts. Using a novel approach integrating
the structurally derived recognition consensus of the RRM with a thermodynamic
description of its multi-register binding, we modeled the saturation
of cellular uridine tracts by this protein. The binding pattern is
remarkably consistent with the experimentally observed transcriptome-wide
cross-link distribution of the full-length hnRNP C on short uridine
tracts. This result re-establishes the RRM as the primary RNA-binding
domain of the hnRNP C tetramer and provides a proof of concept
for interpreting high-throughput interaction data using structural
approaches
Image_1_Repression of Sex4 and Like Sex Four2 Orthologs in Potato Increases Tuber Starch Bound Phosphate With Concomitant Alterations in Starch Physical Properties.TIF
<p>To examine the roles of starch phosphatases in potatoes, transgenic lines were produced where orthologs of SEX4 and LIKE SEX FOUR2 (LSF2) were repressed using RNAi constructs. Although repression of either SEX4 or LSF2 inhibited leaf starch degradation, it had no effect on cold-induced sweetening in tubers. Starch amounts were unchanged in the tubers, but the amount of phosphate bound to the starch was significantly increased in all the lines, with phosphate bound at the C6 position of the glucosyl units increased in lines repressed in StSEX4 and in the C3 position in lines repressed in StLSF2 expression. This was accompanied by a reduction in starch granule size and an alteration in the constituent glucan chain lengths within the starch molecule, although no obvious alteration in granule morphology was observed. Starch from the transgenic lines contained fewer chains with a degree of polymerization (DP) of less than 17 and more with a DP between 17 and 38. There were also changes in the physical properties of the starches. Rapid viscoanalysis demonstrated that both the holding strength and the final viscosity of the high phosphate starches were increased indicating that the starches have increased swelling power due to an enhanced capacity for hydration.</p