| Aspect: identity/complex | Core molecular function | Key regulation/PTMs | Pathway context | Structural features/domains/residues | Representative evidence/assays | Key references with year and URL |
|---|---|---|---|---|---|---|
| SUI2 encodes the α subunit of heterotrimeric eIF2 in *S. cerevisiae*; partner subunits are Sui3/eIF2β and Gcd11/eIF2γ (pqac-00000023) | eIF2 binds GTP and Met-tRNAi\(^Met\) to form the ternary complex (TC), delivering initiator tRNA to the 40S ribosome for 43S/48S preinitiation-complex assembly and start-codon recognition (pqac-00000000, pqac-00000023) | Phosphorylation of eIF2α at conserved Ser51 by Gcn2 inhibits TC formation indirectly by converting eIF2 into an inhibitor of eIF2B-mediated GDP→GTP exchange (pqac-00000000, pqac-00000021, pqac-00000024) | Central node in translation initiation and the yeast general amino acid control / ISR-like stress response; reduced TC selectively derepresses **GCN4** translation while lowering global initiation (pqac-00000014, pqac-00000024) | eIF2α comprises an N-terminal OB-fold, a central α-helical domain, and a C-terminal α/β domain that contacts eIF2γ; Ser51 lies in a mobile loop in the OB-fold (pqac-00000000, pqac-00000023) | Genetic suppressor analysis (Sui\(^-\) mutants), TC-binding/48S studies, cryo-EM-informed models, reporter assays for GCN4 control (pqac-00000000, pqac-00000014, pqac-00000016) | Dever et al., 2016, *Genetics*, https://doi.org/10.1534/genetics.115.186221; Adomavicius et al., 2019, *Nat Commun*, https://doi.org/10.1038/s41467-019-10167-3 |
| eIF2α/Sui2 acts directly within the scanning preinitiation complex (pqac-00000017, pqac-00000018) | Helps stabilize scanning/open and start-recognition/closed states of the PIC; contributes to accuracy of AUG selection versus near-cognate codons such as UUG (pqac-00000003, pqac-00000005, pqac-00000006) | No catalytic activity of its own; function is regulated by phosphorylation state and by residue-specific interactions with mRNA/rRNA/eIF1/eIF5 (pqac-00000005, pqac-00000003) | Part of the eIF2 cycle linking TC loading, scanning, start-codon recognition, and factor recycling by eIF2B/eIF5 (pqac-00000016, pqac-00000024) | R53 contacts rRNA helix 23; Arg55/Arg57 contact mRNA context near the start site; unstructured N-terminal tail interacts with eIF1 in the open PIC and later with eIF5-CTD after AUG recognition (pqac-00000017, pqac-00000018, pqac-00000003) | HIS4-lacZ UUG:AUG reporters, growth phenotypes, plasmid-shuffle SUI2 alleles, β-gal assays, western blots, TC dissociation/recruitment measurements (pqac-00000006, pqac-00000007, pqac-00000018) | Thakur et al., 2020, *Nucleic Acids Res*, https://doi.org/10.1093/nar/gkaa761 |
| eIF2α is the canonical substrate of yeast Gcn2 kinase under amino acid stress and other nutrient stresses (pqac-00000020, pqac-00000025) | When phosphorylated, lowers available TC so scanning 40S subunits reacquire TC more slowly, enabling bypass of inhibitory uORFs in **GCN4** leader and translation of GCN4 ORF (pqac-00000024) | Ser51 phosphorylation is promoted by uncharged tRNAs via Gcn1/Gcn20 and can be influenced upstream by TOR/Tap42, Snf1, and phosphatases Glc7/Sit4 acting on the pathway (pqac-00000020, pqac-00000021, pqac-00000025) | Integrates amino acid starvation, TOR inhibition/rapamycin response, iron deficiency, and intracellular acid stress into translational control (pqac-00000021, pqac-00000025, pqac-00000022) | Ser51 is the key phospho-acceptor residue; phosphorylation increases affinity of eIF2 for eIF2B, explaining inhibitory sequestration of the GEF (pqac-00000016, pqac-00000021) | Phospho-specific western blots, GCN4-lacZ derepression assays, polysome profiling, toeprinting, genetic epistasis with gcn2Δ/gcn1Δ and S51A mutants (pqac-00000014, pqac-00000019, pqac-00000021) | Cherkasova & Hinnebusch, 2003, *Genes Dev*, https://doi.org/10.1101/gad.1069003; Romero et al., 2020, *Sci Rep*, https://doi.org/10.1038/s41598-019-57132-0 |
| SUI2 participates in stress-adaptive translational control beyond classic amino acid starvation (pqac-00000015, pqac-00000025) | Supports selective translation programs that help cells adapt to nutrient and physicochemical stress while globally repressing bulk translation (pqac-00000015, pqac-00000025) | S51A phospho-dead Sui2 abolishes this regulatory switch in tested stress settings (pqac-00000015, pqac-00000013) | Shown for intracellular acid stress and iron deficiency, highlighting broad stress responsiveness of the Gcn2–eIF2α axis in yeast (pqac-00000015, pqac-00000025) | Same conserved Ser51-centered regulatory loop underlies distinct stress outputs (pqac-00000022, pqac-00000013) | Acid-stress growth phenotyping of **sui2-S51A**; iron-starvation analyses of global translation initiation dependence on Gcn2/eIF2α pathway (pqac-00000015, pqac-00000025) | Hueso et al., 2012, *Biochem J*, https://doi.org/10.1042/BJ20111264; Uppala et al., 2018, *FEBS Lett*, https://doi.org/10.1002/1873-3468.13214 |
| Recent systems-level work extends the eIF2α-centered network to additional Gcn2 targets while retaining Sui2/eIF2α phosphorylation as the core output (pqac-00000019) | Confirms eIF2α phosphorylation-dependent derepression of **GCN4** and identifies cooperating translational regulators (e.g., Sui3/eIF2β, Gcn20) (pqac-00000008, pqac-00000019) | In 2021 phosphoproteomics, Sui2-Ser52, Sui3-Ser80, and Gcn20 Thr94/Ser95 were robust Gcn2-dependent sites in rapamycin-treated or leucine-starved cells (pqac-00000008, pqac-00000019) | Places SUI2 within a broader Gcn2-regulated phospho-network affecting translation initiation under TOR inhibition and amino acid stress (pqac-00000019) | Sui2 phosphosite is adjacent to the canonical Ser51 numbering convention used in many studies/antibodies; evidence supports conserved regulatory-site assignment in yeast datasets (pqac-00000008, pqac-00000025) | Quantitative phosphoproteomics, in vitro kinase assays, GCN4-lacZ reporter derepression, and polysome P:M measurements (e.g., Gcn20 phosphomutants changing P:M ratios by −10.6%, −7.6%, or +8.6% in specified conditions) (pqac-00000019) | Dokládal et al., 2021, *Molecular Cell*, https://doi.org/10.1016/j.molcel.2021.02.037 |


*Table: This table compactly summarizes the verified identity, molecular function, regulation, structural features, pathway roles, and supporting evidence for yeast SUI2/eIF2α (UniProt P20459). It is useful as a citation-ready functional annotation artifact grounded only in the gathered evidence and context IDs.*