Many target proteins are thought to be ubiquitinated by only one E3, while others, the tumor suppressor p53 for example, can be ubiquitinated by multiple E3s [ 71, 116, 141].
Proteins can be ubiquitinated at one or multiple K residues with either a single ubiquitin molecule (mono- or multi-monoubiquitination) or a chain of ubiquitin (polyubiquitination).
In patients with mutant SOD1-linked FALS, SOD1-positive aggregates are reported to be ubiquitinated by RING finger-type E3 ubiquitin ligases such as dorfin [30] [33].
It has recently been shown that SUMO chains interact with STUbLs, and can be ubiquitinated by them [21].
A second, alternative hypothesis would be that these plants require multiple related RBR proteins to cope with an increased diversity of substrates to be ubiquitinated in particular cells, tissues or developmental periods.
Several identified proteins with these criteria have been reported to be ubiquitinated in the literature.
Upon coincubation with motile spermatozoa, the solubilized ZPP, which appear to be ubiquitinated, adhered to sperm acrosomal caps and induced acrosomal exocytosis/formation of the acrosomal shroud.
Cat1 was ubiquitinated at multiple sites on lysine residues, at least in part, in the cytoplasmic N-terminal region (Fig. 7, Fig. 8C).
Because NICD ΔANK Mut does not interact with the Snail protein, we hypothesized that Snail would not be ubiquitinated in its presence.
Similarly, the comparison of SwissPalm with ubiquitination databases suggested that proteins that can be palmitoylated also appear to be ubiquitinated.
