Entry created on 1 July 2019 (Revision 1.0) Annotator: Rita Pancsa
Basic protein information
Accession Q07666
Common name Sam68
Gene KHDRBS1
Organism Homo sapiens
Uniprot name KH domain-containing, RNA-binding, signal transduction-associated protein 1
Basic LLPS information
Organelle nuclear body; ribonucleoprotein complex; Sam68 nuclear bodies (SNBs)
Type of experimental evidence
Protein region(s) mediating LLPS
1
-
197
G-rich N-terminal IDR and KH domain
Based on the experimental results of the following publication: 27377249
Molecular features viewer
PDB structures
View on PDBe
Extended LLPS information
Functional description
Sam68 and HNRNPD are essential for the formation of the RNase-sensitive Sam68 nuclear bodies (SNBs). Knockdown of each SNB protein revealed that SNBs are composed of two distinct RNase-sensitive substructures. One substructure is present as a distinct NB, termed the DBC1 body, in certain conditions, and the more dynamic substructure including Sam68 joins to form the intact SNB. HNRNPL acts as the adaptor to combine the two substructures and form the intact SNB through the interaction of two sets of RNA recognition motifs with the putative arcRNAs in the respective substructures. In case of Sam68 the N-terminal GSG disordered domain and the following KH domain are essential for SNB localization and formation. SNBs are RNase sensitive. In vitro LLPS experiments with these constructs are lacking (PMID:27377249).
Literature supporting the LLPS: 27377249
Functional class of membraneless organelle: not known/not clear
Binding partners (at biological protein concentrations)
1) RNA (not only for SNB localization but also for SNB formation)
Type of RNA(s) required/used for the LLPS at biological protein concentrations
cellular RNA
Molecular interaction types contributing to LLPS
protein-RNA interaction (PMID:27377249)
Determinants of phase separation and droplet properties
N/A
Membrane cluster No
Partner-dependent Yes
RNA-dependent Yes
PTM required Not known
Domain-motif interactions No
Discrete oligomerization Yes
Regulation and disease
Post-translational modifications affecting LLPS
Position Residue PTM Effect Reference Modifying enzyme Notes
Isoforms known to affect LLPS
Isoform Effect Reference
All known isoforms containing sequence changes in the LLPS region(s)
Position type Isoform names from UniProt
Disease mutations affecting LLPS
Mutation dbSNP Disease OMIM Effect Reference Notes
Experimental information
Experimental techniques applied to prove/investigate LLPS
In vivo, SNBs disappeared upon a temperature shift from 37 to 32°C for 24 h and reformed when the temperature was returned to 37°C for 3 h (particle size and count by microscopy on change in temperature). Depletion of Sam68 or HNRNPD by RNAi in HeLa cells in vivo resulted in the disappearance of SNBs as detected by immunofluorescence, whereas depletion of the three other proteins (HNRNPL, DBC1, and ZNF346) hardly affected the integrity of SNBs. Based on truncation studies, the GSG domain, particularly the N-terminal-to-KH-domain region (NK region) and the RNA-binding KH domain but not the C-terminal-to-KH-domain region (CK region) in this domain, was required for SNB localization of Sam68. A substantial DBC1 signal was detected when an essential SNB component, either Sam68 or HNRNPD, was knocked down. Furthermore, when HNRNPL was knocked down, the DBC1 signal was detected in nuclear foci distinct from those labeled with Sam68 and HNRNPD (protein localization). Both nuclear foci (the Sam68 substructure and the DBC1 substructure) were sensitive to RNase treatment (enzymatic activity assay). No in vitro results available, LLPS, formation of SNBs may require other factors (PMID:27377249).
Experimental observations supporting the liquid material state of the condensate
temperature-dependence (PMID:27377249) reversibility of formation and dissolution (PMID:27377249)