-
Sbp1 (P10080, YHL034C; historical synonym SSB1/SSBR1) is an RGG/RRM RNA-binding
protein with two RRM domains separated by an RGG box that regulates cytoplasmic
mRNP state transitions between active translation and translationally repressed
states associated with P-bodies and stress granules.
"The literature synthesized here explicitly studies *Saccharomyces cerevisiae* Sbp1/Sbp1p (also referred to historically as Ssb1p) and describes the characteristic architecture of **two RRMs separated by an RGG box**"
-
Sbp1 represses translation initiation by binding the scaffold factor eIF4G;
biochemical mapping implicates its central RGG region in the eIF4G interaction.
"Biochemical evidence demonstrates that Sbp1 **directly binds eIF4G**, and that the **RGG motif is required and sufficient** for that interaction in vitro. In particular, an isolated Sbp1 RGG region (residues **121–180**) bound GST-eIF4G in binding assays, whereas deletion of the RGG region impaired binding"
-
Sbp1 binds mRNAs with a positional preference for the 5' UTR rather than strong
sequence specificity, as shown by transcriptome-wide CLIP; its CLIP target set is
most similar to Dhh1's.
"A global yeast mRNP study using CLIP identified Sbp1 among a set of PB/SG-associated RBPs (with Pat1, Lsm1, Dhh1) and found that Sbp1 exhibits **positional specificity** on transcripts: Sbp1 binding shows a clear preference for the **5′ UTR**, rather than strong sequence specificity"
-
Sbp1 is largely cytoplasmic in mid-log phase and accumulates in P-bodies and
stress granules under stress conditions or upon overexpression, where
overexpression reduces polysomes consistent with translational repression.
"Sbp1 itself is largely cytoplasmic in mid-log phase and accumulates in PBs under stress conditions (e.g., glucose deprivation/high cell density) or upon overexpression, consistent with conditional relocalization during mRNP remodeling"
-
Sbp1 is a P-body disassembly factor during recovery from stress: delta-sbp1 cells
are defective in disassembly of Edc3-, Dhh1-, and Scd6-marked foci, and purified
Sbp1 interacts with Edc3 and reduces Edc3 assemblies in vitro.
"Recent work supporting a PB disassembly role shows that purified Sbp1 can interact with Edc3 domains (LSm-FDF and YjeF-N in the cited excerpt), in RNase-treated conditions (supporting RNA-independent detectability), and that Sbp1 can reduce Edc3 assemblies in vitro—supporting a mechanistic basis for PB dissolution"
-
The RGG motif is required for Sbp1's P-body disassembly activity, and an
arginine-methylation-defective mutant (13 Arg-to-Ala in the RGG motif) fails to
rescue disassembly, implicating arginine residues and methylation state.
"Complementation and mutant analyses indicate that the **RGG motif is required** for rescuing PB disassembly defects, and an “arginine methylation defective” mutant (13 Arg→Ala in the RGG motif) fails to rescue, implicating arginine residues (and plausibly methylation state) in function"