J-chain and p53 gene expression in KIS-1 and MZL-1 lymphomas. (A) Absence of J-chain gene expression in B lymphocytes carrying the t(9;14) translocation. Human B-cell lines (BJA-B, Raji, Ramos, HS-Sultan), myeloma cell lines (U226, RPMI 8226), KIS-1 cells and mononuclear blood cells of patient MZL-1 as well as of a control individual (MNC) were analyzed by RNase protection assay for J-chain and S16 mRNA expression. (B) Normal p53expression in tumors overexpressing PAX-5. The p53 mRNA levels were quantitated by RNase protection analysis in a subset of the cells studied in panel A. MB-238 refers to the tumor that exhibits the highest PAX-5 expression level within a large medulloblastoma collection.20 The KIS-1 cells carry a mutation resulting in a truncated p53 mRNA (p53▵) that is detected on the longer autoradiographic exposure shown to the left.