Northern blot analysis for IgH and Igκ transcription in L1236 cells. Total cellular RNA of the cell lines was separated on an agarose gel, transferred to a nylon filter, and probed with cDNA clones for Cγ (A, right) and Cκ (B, top, left), respectively. Although the LCL L1309 does express the membrane bound Cγ heavy chain transcript and the secreted Cγ heavy chain transcript (A) as well as the κ light chain transcript (B), neither IgG nor Igκ transcripts are detected in L1236 cells (A, right: ethidium bromide staining of the gel before blotting; B, bottom: hybridization for GAPDH transcripts to control quality of total RNA). The cell lines U937 and CO serve as negative controls for Ig gene transcripts. To increase the sensitivity of Northern blot analysis for Cκ, mRNA was separated on an agarose gel, transferred to a nylon filter, and probed with a cDNA clone (B, left, top). Again, no hybridization signal was obtained in L1236 mRNA. L1309 cells serve as positive control. CO cells serve as negative control. Hybridization with a GAPDH probe to check quality and amount of mRNA showed that approximately equal amounts of intact RNA were loaded on the gel for the various cell lines (B, bottom).