| Aspect | Evidence/Key finding | Representative sources (with year, journal) | URL/DOI |
|---|---|---|---|
| Target identity / family | **prg-1** in **Caenorhabditis elegans** encodes the worm **Piwi-class Argonaute** that binds piRNAs/21U-RNAs; this matches UniProt P90786 (Piwi-like protein 1) and the Argonaute/Piwi family assignment. PRG-1 is described as the **single functional Piwi protein** in C. elegans. (pqac-00000008, pqac-00000011) | Pastore et al., 2024, *Cell Reports*; Lee et al., 2012, *Cell* | https://doi.org/10.1016/j.celrep.2024.113692; https://doi.org/10.1016/j.cell.2012.06.016 |
| Primary molecular function | PRG-1 is a **small-RNA-guided surveillance Argonaute**: PRG-1/piRNA complexes base-pair with germline transcripts and **initiate silencing indirectly** by recruiting RdRP-dependent secondary siRNA production rather than acting mainly as a direct mRNA-cleaving enzyme. PRG-1 is required to **initiate**, but not maintain, silencing of piRNA-targeted transgenes. (pqac-00000001, pqac-00000003, pqac-00000010) | Lee et al., 2012, *Cell*; de Albuquerque et al., 2015, *Developmental Cell*; Shirayama et al., 2012, *Cell* | https://doi.org/10.1016/j.cell.2012.06.016; https://doi.org/10.1016/j.devcel.2015.07.010; https://doi.org/10.1016/j.cell.2012.06.015 |
| Catalytic activity vs non-slicer role | Although Argonautes are RNase H-like proteins, available evidence emphasizes that **PRG-1 catalytic/slicer activity is not required for piRNA-induced silencing** in the canonical pathway; instead, PRG-1 functions primarily as a **target-recognition and recruitment platform** for downstream silencing factors. (pqac-00000000, pqac-00000011) | Seth, 2016, dissertation; Lee et al., 2012, *Cell* | https://doi.org/10.13028/m2c30k; https://doi.org/10.1016/j.cell.2012.06.016 |
| Small-RNA cofactor: piRNAs / 21U-RNAs | PRG-1 binds **21U-RNAs**, the C. elegans piRNAs. Mature piRNAs are typically **~21 nt** and strongly biased for **5′ U**. More than **15,000** 21U-RNAs/type I piRNA loci are reported, largely organized in **two large clusters on chromosome IV**; dissertation/database-style summaries report **>30,000** total piRNAs when broader classes are included. (pqac-00000008, pqac-00000011, pqac-00000000) | Pastore et al., 2024, *Cell Reports*; Lee et al., 2012, *Cell*; Seth, 2016, dissertation | https://doi.org/10.1016/j.celrep.2024.113692; https://doi.org/10.1016/j.cell.2012.06.016; https://doi.org/10.13028/m2c30k |
| piRNA targeting rules | piRNA targeting is **broad and mismatch-tolerant**, with imperfect but extensive base pairing sufficient to trigger downstream 22G-RNA synthesis; this enables transcriptome-wide surveillance of germline RNAs and foreign/non-self detection. (pqac-00000001, pqac-00000016) | Lee et al., 2012, *Cell*; Weiser & Kim, 2019, *Annual Review of Genetics* | https://doi.org/10.1016/j.cell.2012.06.016; https://doi.org/10.1146/annurev-genet-112618-043505 |
| Upstream biogenesis: transcriptional factors | Type I piRNA genes are associated with the **Ruby motif** and require factors including **PRDE-1, SNPC-4, TOFU-4, TOFU-5** for promoter activity/precursor accumulation. (pqac-00000008, pqac-00000016) | Pastore et al., 2024, *Cell Reports*; Weiser & Kim, 2019, *Annual Review of Genetics* | https://doi.org/10.1016/j.celrep.2024.113692; https://doi.org/10.1146/annurev-genet-112618-043505 |
| Upstream biogenesis: precursor processing | C. elegans piRNA precursors are short **capped small RNAs (csRNAs)** of about **25–29 nt**. Processing includes removal of the **5′ cap and first two nucleotides** by a Schlafen-domain nuclease, **3′ trimming by PARN-1**, and **3′ terminal 2′-O-methylation by HENN-1**. (pqac-00000008, pqac-00000012) | Pastore et al., 2024, *Cell Reports* | https://doi.org/10.1016/j.celrep.2024.113692 |
| Biogenesis quality control / recent mechanism | In **parn-1** mutants, untrimmed pre-piRNAs accumulate and are aberrantly converted into **anti-piRNAs** (17–19 nt, often starting with **A or G**) via **RDE-3** and **EGO-1**, showing that correct piRNA maturation is needed to prevent erroneous RdRP engagement. (pqac-00000012, pqac-00000017) | Pastore et al., 2024, *Cell Reports* | https://doi.org/10.1016/j.celrep.2024.113692 |
| Secondary small RNAs | PRG-1/piRNA target recognition recruits **RNA-dependent RNA polymerases (RdRPs)** to generate **secondary 22G-RNAs**, which are the principal downstream effectors of silencing. Loss of prg-1 causes depletion of subsets of 22G-RNAs at normally silent loci. (pqac-00000001, pqac-00000003, pqac-00000018) | Lee et al., 2012, *Cell*; de Albuquerque et al., 2015, *Developmental Cell* | https://doi.org/10.1016/j.cell.2012.06.016; https://doi.org/10.1016/j.devcel.2015.07.010 |
| Downstream effector machinery | The PRG-1 pathway interfaces with the **Mutator complex** and **WAGO Argonautes**. PRG-1-triggered 22G-RNAs are loaded onto WAGOs, including the nuclear Argonaute **HRDE-1**, to enforce heritable gene silencing/RNAe. Key associated factors include **MUT-7**, **RDE-3**, RdRPs, and WAGO proteins. (pqac-00000003, pqac-00000006, pqac-00000010, pqac-00000016) | de Albuquerque et al., 2015, *Developmental Cell*; Shirayama et al., 2012, *Cell*; Weiser & Kim, 2019, *Annual Review of Genetics* | https://doi.org/10.1016/j.devcel.2015.07.010; https://doi.org/10.1016/j.cell.2012.06.015; https://doi.org/10.1146/annurev-genet-112618-043505 |
| Subcellular localization | PRG-1 localizes to **perinuclear germ granules / P granules**, and recent work indicates association with **P and Z granule compartments**, with enrichment in **Z granules**. Mutator foci act adjacent to these granules. (pqac-00000005, pqac-00000007, pqac-00000003) | Wallis & Phillips, 2025, *bioRxiv*; de Albuquerque et al., 2015, *Developmental Cell* | https://doi.org/10.1101/2025.05.12.653514; https://doi.org/10.1016/j.devcel.2015.07.010 |
| Germline expression / tissue context | PRG-1 is **germline-restricted**; expression is absent in animals lacking a germline. Its core physiological role is therefore in the **germline**, where it supports fertility and genome defense. (pqac-00000002, pqac-00000008) | Almeida, 2012; Pastore et al., 2024, *Cell Reports* | Unknown journal; https://doi.org/10.1016/j.celrep.2024.113692 |
| Biological process: genome defense | The canonical role of PRG-1/piRNAs is to **safeguard germline genome integrity** by targeting foreign sequences, transgenes, and some transposable elements, triggering epigenetic and post-transcriptional silencing programs. (pqac-00000008, pqac-00000010, pqac-00000016) | Pastore et al., 2024, *Cell Reports*; Shirayama et al., 2012, *Cell*; Weiser & Kim, 2019, *Annual Review of Genetics* | https://doi.org/10.1016/j.celrep.2024.113692; https://doi.org/10.1016/j.cell.2012.06.015; https://doi.org/10.1146/annurev-genet-112618-043505 |
| Transposon silencing specificity | PRG-1 has a **surprisingly limited direct transposon spectrum** in C. elegans compared with some other animals; **Tc3** is the clearest established PRG-1-dependent transposon target, although PRG-1 is still important for broader genome surveillance and de novo transposon silencing states. (pqac-00000001, pqac-00000003) | Lee et al., 2012, *Cell*; de Albuquerque et al., 2015, *Developmental Cell* | https://doi.org/10.1016/j.cell.2012.06.016; https://doi.org/10.1016/j.devcel.2015.07.010 |
| Epigenetic inheritance / RNAe | PRG-1 initiates **RNA-induced epigenetic silencing (RNAe)** and establishment of a heritable memory of **non-self** sequences; **maintenance** of the silent state can persist without continued PRG-1, relying on WAGO/HRDE-1 and chromatin factors. (pqac-00000010, pqac-00000016) | Shirayama et al., 2012, *Cell*; Weiser & Kim, 2019, *Annual Review of Genetics* | https://doi.org/10.1016/j.cell.2012.06.015; https://doi.org/10.1146/annurev-genet-112618-043505 |
| Maternal contribution | **Maternal piRNAs/PRG-1 activity** are critical when 22G-RNA silencing programs must be established de novo; maternal 21U-RNAs are required for efficient initiation of transposon silencing and normal germline development after re-establishment of endo-siRNA pathways. (pqac-00000003, pqac-00000006) | de Albuquerque et al., 2015, *Developmental Cell* | https://doi.org/10.1016/j.devcel.2015.07.010 |
| Phenotypes of prg-1 loss | Loss of prg-1 causes **reduced brood size**, **temperature-sensitive sterility**, progressive **mortal germline / germline immortality defects**, and altered germline morphology. (pqac-00000002, pqac-00000004, pqac-00000007) | Almeida, 2012; Montgomery et al., 2021, *Cell Reports*; Wallis & Phillips, 2025, *bioRxiv* | Unknown journal; https://doi.org/10.1016/j.celrep.2021.110101; https://doi.org/10.1101/2025.05.12.653514 |
| Quantitative figure-supported evidence | In Lee et al. Figure 1, WT small RNAs include substantial **21U-RNA** and **22G-RNA** fractions, whereas **prg-1 mutants lose the 21U-RNA fraction (shown as 0%)** and display strong depletion of 22G-RNAs at WAGO targets, visually supporting PRG-1’s upstream role in secondary silencing. (pqac-00000018, pqac-00000011) | Lee et al., 2012, *Cell* | https://doi.org/10.1016/j.cell.2012.06.016 |
| Quantitative transposon data | In de Albuquerque et al., **prg-1 mutants** alone showed **very low Tc1 excision/reversion frequency (~10^-5)**, whereas **prg-1; hrde-1 double mutants** showed an approximately **100-fold increase** in Tc1 excision, supporting synergistic action of PRG-1 with downstream nuclear silencing machinery. (pqac-00000006) | de Albuquerque et al., 2015, *Developmental Cell* | https://doi.org/10.1016/j.devcel.2015.07.010 |
| Genome context statistic | Transposable elements comprise approximately **15% of the C. elegans genome**, providing the genomic context for PRG-1/piRNA-mediated genome surveillance. (pqac-00000009) | Fischer, 2024, *DNA* | https://doi.org/10.3390/dna4020007 |
| Emerging non-canonical relevance | Recent disease-model work found that perturbing piRNA biogenesis genes in C. elegans neuronal α-synuclein models can improve neurodegenerative phenotypes, but this is best interpreted as **pathway repurposing in a model system**, not as the primary annotated function of PRG-1, which remains germline piRNA surveillance. (pqac-00000013, pqac-00000015) | Huang et al., 2023, *Nature Communications* | https://doi.org/10.1038/s41467-023-41881-8 |


*Table: This table summarizes core functional-annotation facts for C. elegans PRG-1/Piwi (UniProt P90786), including mechanism, pathway placement, localization, phenotypes, and quantitative findings. It is designed as a quick evidence map linking each annotation-relevant claim to representative cited sources and URLs.*