Truncated μHC is expressed in a L^−/− hybridoma. (A) Genomic alterations in hybridoma Sp3, identified by long-range PCR, cloning, and sequencing (see supplemental Table 1) show that sμ (thick black line), Cμ1, and all but 24 bp of Cμ2 are missing. Immediately adjacent to the remaining sequence of Cμ2 are 220 bp of sγ3 (thick red line). Primers for PCR amplification and nested reamplification are indicated by . (B) Intracellular staining of Sp3 and NSO, the Ig-negative fusion partner, with FITC-conjugated anti-IgM (green) followed by DAPI (blue). (C) Sp3 smears compared with a control IgM,κ-producing hybridoma-stained with PAS, showing vacuoles in purple-magenta, and hematoxylin, showing the nuclei in blue.