TRIM21 and infection: Intriguingly, while Lys-7 ubiquitylation by TRIM21 is critical for p62 oligomerization and protein sequestration (Pan et al., 2016), a K13R mutant was still ubiquitylated in HEK293T cells (Pan et al., 2016), indicating that modification at Lys-13 may play a unique role during infection.