Journal of Cell Science 116, e404-e404 (2003)
Copyright © 2003 The Company of Biologists Limited
An RNA-binding ubiquitin ligase
RNA-binding proteins play critical roles in various aspects of cell
function, such as splicing, transcription termination and mRNA storage. They
are similarly essential for viruses whose replication strategies involve RNA
intermediates. In a search for proteins that bind to hepatitis B virus (HBV)
RNAs, Stefan Kreft and Michael Nassal have identified a human RNA-binding
protein, hRUL138, that looks like nothing yet seen (see
p. 605). hRUL138 is a 138 kDa
cytoplasmic protein that is expressed in most tissues and could be associated
with the ER. It contains a novel RNA-binding domain in which the only
recognizable motif is a coiled-coil region. Remarkably, hRUL138 also contains
the RING-H2 signature characteristic of certain ubiquitin ligases (E3
enzymes). Indeed, Kreft and Nassal show that this has self- and
trans-ubiquitin-ligase activity in vitro and can drive proteasome-mediated
degradation of hRUL138 in vivo. The cellular target RNA for hRUL138 is not yet
clear; however, the unusual combination of RNA-binding and ubiquitin ligase
activities in one protein raises some interesting possibilities. Other
RNA-binding proteins or RNPs, for example, could be targets of the hRUL138
ubiquitin ligase, and it might use RNAs to increase target specificity.

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Related articles in JCS:
- hRUL138, a novel human RNA-binding RING-H2 ubiquitin-protein ligase
- Stefan G. Kreft and Michael Nassal
JCS 2003 116: 605-616.
[Abstract]
[Full Text]