Expression of Ubr5 in B cells and generation of conditional Ubr5 HECT domain knockout model. (A) UBR5 domain map (blue = UBA, black = NLS, red = UBR, blue = MLLE, and purple = HECT) showing the frequency of UBR5 mutations in lymphoma patients. Orange = nonsense/frameshift; green = missense. (B) Frequency of all genes mutated in addition to UBR5 mutations in MCL patients. (C) Relative qRT-PCR and (D) western blot expression of UBR5 within different B-cell populations: pro-B cells (B220⁺IgM⁻ckit⁺), pre-B cells (B220⁺IgM⁻CD25⁺), immature B cells (B220⁺IgM^loIgD⁻) from the BM, and transitional (B220⁺CD93⁺), marginal zone B cells (B220⁺CD21⁺CD23⁻), and follicular B cells (B220⁺CD21⁺CD23⁺) isolated from the spleen of 6-week-old WT C57Bl6 mice. (E) Schematic of targeting strategy used to insert loxP sites flanking exon 58 of Ubr5. (F) Relative expression of Ubr5 and Ubr5 HECT domain by qRT-PCR in spleen B220⁺ cells. (G) Sequencing data of exons 57-59 of Ubr5 from Ubr5 WT and Ubr5 HECT mice.