Figure 4.

Catalytically inactive Lig4 is only moderately deficient in CSR. (A) Western blot of murine Lig4 expressed in Lig4−/− CH12F3 cells. (B) CSR efficiency (percentage of IgA-positive cells, assessed by flow cytometry) in mouse CH12F3 cells expressing WT Lig4, catalytically inactive Lig4 (dLig4), or no Lig4. Error bars indicate SE of three independent experiments. (C) Sensitivity of the same panel of cell strains to calicheamicin was assessed. Briefly, cells were plated in 24 well plates into complete medium with increasing doses of calicheamicin. After 7 days, MTT was added, and cell survival assessed by colorimetry. In B, student's T test comparing joining rates between vector and Lig4, or vector K273S were performed; ****P < 0.0001; in two-tailed unpaired t test. Survival assay was performed three times in duplicate.