PATL1

PATL1 (Pat1b) is a multi-domain scaffold protein that orchestrates cytoplasmic mRNA turnover by physically coupling deadenylation to decapping (PMID:20584987). Through at least three independent domains it bridges the Ccr4-Caf1-Not deadenylation complex, the Dcp1-Dcp2 decapping enzymes, the RNA helicase Rck, and Lsm1; tethering Pat1b to a reporter mRNA promotes both deadenylation and decapping, repressing expression (PMID:20584987, PMID:20852261). It nucleates processing body (P body) assembly via an aggregation-prone N-terminal domain, with an acidic domain setting P body size, and is required for P body formation (PMID:17936923, PMID:20584987). Within this process PATL1 acts downstream of Rck in a stepwise order: Rck first suppresses translation, then Pat1b triggers P body assembly and decapping, with the Rck RecA-like domain engaging the Pat1b N-terminal acidic domain (PMID:23535175). PATL1 is also a nucleocytoplasmic shuttling protein exported through a CRM1-dependent NES, where nuclear PATL1 forms a distinct complex with the Lsm2-8 heptamer and U6 snRNA, connects to SART3 and U4/U6.U5 tri-snRNP components in Cajal bodies, and regulates alternative splicing; its depletion upregulates AU-rich-element-enriched mRNAs and skews regulated exon skipping (PMID:22090346, PMID:28768202). Beyond RNA metabolism, PATL1 interacts with the general transcription factor TFIIE to facilitate transcription of hERG, influencing cardiomyocyte action potential duration (PMID:36608291).

1. 2007 Medium

   Established that PATL1 is a bona fide P body component whose presence is required for P body formation, placing it at the heart of cytoplasmic mRNA storage/decay foci.

   Evidence Tagged PatL1 co-localization with Lsm1, Rck/p54 and Dcp1 plus RNAi knockdown scored for P body formation

   PMID:17936923

   Open questions at the time

   • Did not define which domains drive P body nucleation
   • No biochemical demonstration of direct partner binding
2. 2010 High

   Resolved how PATL1 acts molecularly by showing it is a scaffold connecting deadenylation and decapping machineries, answering whether it merely resides in P bodies or actively drives decay.

   Evidence Reciprocal co-IP of Ccr4-Caf1-Not, Dcp1-Dcp2, Rck and Lsm1, domain deletion mapping, and tethering assays measuring deadenylation/decapping in HeLa cells

   PMID:20584987 PMID:20852261

   Open questions at the time

   • Did not establish target mRNA selectivity genome-wide
   • Stepwise order of recruitment relative to Rck not yet defined
3. 2010 Medium

   Mapped the structural determinants of P body biogenesis to an N-terminal aggregation-prone domain that nucleates assembly and an acidic domain that controls foci size.

   Evidence Domain deletion/mutation analysis with P body formation readout in human cells

   PMID:20584987

   Open questions at the time

   • Molecular basis of the aggregation propensity not determined
   • No in vitro reconstitution of nucleation
4. 2011 Medium

   Revealed an unanticipated nuclear life for PATL1, showing it shuttles via a CRM1-dependent NES and occupies distinct nuclear compartments, expanding its role beyond cytoplasmic decay.

   Evidence Leptomycin B and spliceostatin A treatment, immunofluorescence, and domain mapping of nuclear retention

   PMID:22090346

   Open questions at the time

   • Functional consequence of nuclear localization not yet established
   • Identity of nuclear binding partners undefined
5. 2012 Medium

   Identified ALG-2 (PDCD6) as a Ca2+-dependent partner of PATL1, suggesting a link between calcium signaling and P body composition.

   Evidence In silico motif screening, Far-Western blotting, endogenous co-immunoprecipitation, and co-localization with DCP1A at P bodies

   PMID:22437941

   Open questions at the time

   • No functional consequence of the PATL1-ALG-2 interaction established
   • Calcium dependence of the interaction in cells not demonstrated
6. 2013 High

   Defined a stepwise P body assembly pathway, distinguishing Rck's translational suppression from PATL1's downstream role in triggering foci assembly and decapping.

   Evidence Interaction-deficient point mutations, co-IP, RNAi knockdown with rescue, tethering assays, and immunofluorescence

   PMID:23535175

   Open questions at the time

   • Kinetics of the ordered assembly not directly measured
   • Whether the order generalizes to all target mRNAs unknown
7. 2017 High

   Demonstrated that nuclear PATL1 forms a distinct Lsm2-8/U6 snRNA/SART3 complex in Cajal bodies and regulates alternative splicing, giving the nuclear pool a concrete mechanistic function.

   Evidence Reciprocal co-IP, immunofluorescence, RNAi depletion, and RNA sequencing for mRNA levels and splicing changes

   PMID:28768202

   Open questions at the time

   • Mechanism by which PATL1 selects exons with weak donor sites unresolved
   • Direct contact with splicing machinery vs. indirect effect not separated
8. 2023 Medium

   Connected PATL1 to transcriptional control by showing it binds TFIIE and promotes hERG expression, linking the protein to cardiomyocyte electrophysiology.

   Evidence C. elegans forward genetic screen, RNAi in SH-SY5Y and hiPSC-CMs, co-IP with TFIIE, dual-luciferase reporter, and electrophysiology

   PMID:36608291

   Open questions at the time

   • PATL1 and PATL2 contributions not always separated
   • Whether TFIIE binding is direct and gene-selective mechanism unresolved

• How PATL1 partitions and is regulated between its cytoplasmic decay, nuclear splicing, and transcriptional roles, and what determines target selectivity in each, remains unresolved.
• No integrated regulatory model linking the three compartmental functions
• Signals controlling nucleocytoplasmic shuttling in vivo unknown
• Target specificity determinants for decay vs. splicing vs. transcription undefined