Deregulation of PAX-5 transcription by t(9;14) translocations. PAX-5 transcript levels were quantitated by RNase protection assay in total RNA isolated from mononuclear blood cells of patient MZL-1, from the large-cell lymphoma cell line KIS-1, from the B-cell lines Raji and BJA-B, from mononuclear blood cells of two patients diagnosed with B-CLL and from control HeLa cells. The 5′ ends of the PAX-5A (A) and PAX-5B (B) transcripts, the spliced mRNA sequences of the downstream paired domain (C) and the hybrid Sμ-PAX5B transcripts (D) were mapped with the riboprobes depicted below. The size of the expected RNase-protected fragments is given in numbers of nucleotides. pUC19 DNA digested withMspI was used as end-labeled DNA size marker (lane M; sizes given in nucleotides). Transcripts coding for the small ribosomal protein S1632 were comapped and used as an internal reference for quantitation of the PAX-5 RNA signals by PhosphorImager analysis. The induction of the different PAX-5transcripts in the KIS-1 and MZL-1 cells was calculated relative to the average PAX-5 expression level of the two B cell lines Raji and BJA-B and is shown below the relevant part of the S16 autoradiograph. The Sμ promoter lacks a TATA-box28 and thus results in heterogeneous transcription initiation in MZL-1 cells (D). Abbreviations: E, EcoRI; B, BamHI; EA,EagI; S, Sau3A; P, PstI.