RPL13A

RPL13A (uL13) is a 60S ribosomal protein that doubles as an extraribosomal regulator of inflammatory gene expression: following IFN-γ stimulation it is released from ribosomes and assembles into the GAIT complex to translationally silence inflammation-related mRNAs (PMID:22771119). In its free, ribosome-released state RPL13A is stabilized by GAPDH, which acts as a chaperone shielding it from proteasomal degradation; this protection is abolished when GAPDH is S-nitrosylated at Cys247 (induced by oxidized LDL plus IFN-γ), leading to degradation of essentially the entire cellular pool of L13a and loss of GAIT-mediated translational control (PMID:22771119). The RPL13A genomic locus is tandemly organized with RPS11 and harbors four intronic snoRNAs (U32–U35) within introns 2, 4, 5, and 6, co-localizing these non-coding RNAs with the protein-coding gene (PMID:10580157). Free RPL13A is additionally a substrate for PARP1/PARP2-mediated ADP-ribosylation in vitro, a modification absent on ribosome-bound RPL13A [PMID:bio_10.1101_2025.09.15.676193].

1. 1999 Medium

   Establishing the architecture of the RPL13A locus revealed it is not a simple protein-coding gene but a host for four intronic snoRNAs co-localized with the coding sequence, framing the locus as a multi-output genetic unit.

   Evidence Genomic sequencing and comparative human/mouse analysis of the RPL13A/RPS11 region

   PMID:10580157

   Open questions at the time

   • Does not assign function to the intronic snoRNAs U32–U35
   • Does not establish whether snoRNA biogenesis depends on RPL13A transcription or splicing
   • No link between locus architecture and the extraribosomal protein function
2. 2012 High

   Connecting RPL13A stability to a redox-sensitive chaperone resolved how the extraribosomal GAIT-forming pool of L13a is maintained and how it is dismantled, linking a specific GAPDH post-translational modification to defective translational control of inflammation.

   Evidence Co-immunoprecipitation of the GAPDH–L13a complex, proteasome-inhibitor rescue, GAPDH Cys247 site-directed mutagenesis, S-nitrosylation detection, and translational reporter assays under oxLDL/IFN-γ

   PMID:22771119

   Open questions at the time

   • Does not define the structural basis of GAPDH–L13a recognition
   • Does not identify the E3 ligase or degron driving proteasomal turnover of free L13a
   • Does not establish how release from the ribosome is itself triggered
3. 2025 Low

   Identifying free RPL13A as a major PARylation target among 60S proteins introduced a candidate post-translational layer distinguishing the ribosome-bound from the extraribosomal state, since the modification occurs only on released protein.

   Evidence In vitro ADP-ribosylation assays with radiolabeled NAD+ on isolated subunits and total ribosomal proteins, comparing bound versus free RPs, with HPF1 co-factor titration (preprint)

   PMID:bio_10.1101_2025.09.15.676193

   Open questions at the time

   • In vitro reconstitution only; the modification is not validated in cells
   • Functional consequence of PARylation for GAIT assembly or L13a stability is unknown
   • Modified residues are not mapped beyond a serine/tyrosine preference conferred by HPF1

• How the multiple post-translational and chaperone inputs (GAPDH protection, S-nitrosylation-triggered degradation, PARylation) are integrated to govern the balance between ribosomal and GAIT-bound RPL13A remains unresolved.
• No unified model coupling ribosome release, PARylation, and GAPDH-dependent stability
• Relationship between the intronic snoRNA outputs and protein-level regulation is uncharacterized