| Aspect | Key findings | Best supporting citations | Primary source (author year journal) and URL/date when available |
|---|---|---|---|
| Identity/domains | **CRH1 = YGR189C** in *Saccharomyces cerevisiae* encodes Congo red hypersensitive protein 1, a **GH16-family** cell-wall protein with an N-terminal secretion signal, Ser/Thr-rich region, conserved **DE(I/L)DXE** catalytic motif, and predicted **GPI-anchor** attachment sequence; these features match UniProt P53301 and support a cell-surface remodeling role. | (pqac-00000001, pqac-00000003, pqac-00000007) | Rodríguez-Peña et al. 2000, *Molecular and Cellular Biology* (May 2000). https://doi.org/10.1128/mcb.20.9.3245-3255.2000 |
| Enzymatic activity | CRH1 is experimentally supported as a **transglycosylase/transglycosylase-like enzyme** that forms covalent **chitin–glucan cross-links** in the yeast cell wall; catalytic residues in the conserved motif are required for function, and mutating them abolishes complementation of Congo red sensitivity. | (pqac-00000002, pqac-00000004, pqac-00000005) | Cabib et al. 2007, *Molecular Microbiology* (Feb 2007). https://doi.org/10.1111/j.1365-2958.2006.05565.x; Rodríguez-Peña et al. 2000, *MCB* (May 2000). https://doi.org/10.1128/mcb.20.9.3245-3255.2000 |
| Substrates/acceptors | Crh1/Crh2 transfer **short nascent chitin fragments** onto both **β(1→6)-glucan** and **β(1→3)-glucan**. In vitro family data indicate soluble chitin derivatives such as **glycol chitin** can serve as donors, with the donor reducing end joined to the acceptor non-reducing end and a minimal acceptor length of ~2 sugar residues. | (pqac-00000009, pqac-00000010, pqac-00000014) | Cabib 2009, *Eukaryotic Cell* (Nov 2009). https://doi.org/10.1128/EC.00228-09; summarized with biochemical details in later family analysis (pqac-00000010). |
| Cellular localization | Crh1 localizes to the **cell wall/cell cortex** at **polarized growth sites**, including the site of bud emergence, **mother–bud neck**, bud scars, mating projections, and spore envelope; localization overlaps with chitin-rich regions and supports direct participation in wall assembly. | (pqac-00000003, pqac-00000004, pqac-00000013) | Rodríguez-Peña et al. 2000, *MCB* (May 2000). https://doi.org/10.1128/mcb.20.9.3245-3255.2000; Cabib et al. 2007, *Molecular Microbiology* (Feb 2007). https://doi.org/10.1111/j.1365-2958.2006.05565.x |
| Regulation | **CRH1 expression is cell-cycle regulated** with peaks around **G1** and **M/G1**, rises transiently **4–5× after pheromone release**, and is induced at **38°C** through the **cell integrity pathway**; this heat induction is lost in **slt2Δ**, linking CRH1 to cell-wall stress signaling. | (pqac-00000004, pqac-00000005, pqac-00000015) | Rodríguez-Peña et al. 2000, *MCB* (May 2000). https://doi.org/10.1128/mcb.20.9.3245-3255.2000; Cabib et al. 2007, *Molecular Microbiology* (Feb 2007). https://doi.org/10.1111/j.1365-2958.2006.05565.x |
| Mutant phenotypes | **crh1Δ** cells are hypersensitive to **Congo red** and **Calcofluor white**; the **crh1Δ crh2Δ** double mutant is more severely affected, genetically aggravates **fks1Δ** and **gas1Δ** wall defects, and shows altered glucan organization rather than major changes in total chitin content. Catalytic-site mutants fail to complement these phenotypes. | (pqac-00000001, pqac-00000002, pqac-00000005, pqac-00000013) | Rodríguez-Peña et al. 2000, *MCB* (May 2000). https://doi.org/10.1128/mcb.20.9.3245-3255.2000; Cabib et al. 2007, *Molecular Microbiology* (Feb 2007). https://doi.org/10.1111/j.1365-2958.2006.05565.x |
| Quantitative cross-linking data | In wild type, total cell-wall chitin was estimated at roughly **36–43% free**, **15–22% linked to β(1→6)-glucan**, and **37–44% linked to β(1→3)-glucan** depending on assay. In **crh1 crh2** double mutants, **virtually all chitin is free**; other summaries report WT partitioning of **31% free, 44% β(1→3)-linked, 25% β(1→6)-linked**, and **~2×** higher alkali-soluble glucan in double mutants. | (pqac-00000009, pqac-00000010, pqac-00000012, pqac-00000016) | Cabib 2009, *Eukaryotic Cell* (Nov 2009). https://doi.org/10.1128/EC.00228-09; summary/secondary extraction of values in later family overview (pqac-00000010). |
| Key methods | Functional assignment relied on **gene deletion/overexpression**, **catalytic-site mutagenesis**, **GFP/HA localization**, **laminarinase release from walls**, radiolabeling with **[^14C]-glucosamine/glucose**, **carboxymethylation**, selective **β(1→3)- and β(1→6)-glucanase** digestion, **Sephacryl S-300 chromatography**, and newer **curdlan-affinity** and **chitosan extraction** assays. These orthogonal methods converged on the same conclusion that Crh1/Crh2 generate all detectable chitin–glucan cross-links. | (pqac-00000008, pqac-00000009, pqac-00000012, pqac-00000015) | Cabib et al. 2007, *Molecular Microbiology* (Feb 2007). https://doi.org/10.1111/j.1365-2958.2006.05565.x; Cabib 2009, *Eukaryotic Cell* (Nov 2009). https://doi.org/10.1128/EC.00228-09 |


*Table: This table summarizes the core functional annotation of *S. cerevisiae* CRH1/YGR189C (UniProt P53301), including identity, enzymatic role, localization, regulation, mutant phenotypes, quantitative cross-linking data, and the key experiments that support those conclusions.*