The 11q13 breakpoint region of t(11;14) (q13;q32), translocated to the Ig heavy chain locus at 14q32, has been designated as BCL-1 for B-cell leukemia/lymphoma-1, but the nature of the transcriptional unit has long remained unclear. Recently, the PRAD1 gene encoding cyclin D1, isolated from the 11q13 region, was proposed as a candidate BCL-1 gene on the basis of chromosome walking and concordant overexpression of PRAD1 mRNA in cell lines with t(11;14)(q13;q32). We report here molecular analysis of a variant translocation at the BCL-1 locus, t(11;22)(q13;q11), showing juxtaposition of the Ig light chain gene, Ig lambda, to the PRAD1 gene at its 3′ end, resulting in overexpression of PRAD1 mRNA. Because only the PRAD1 gene is present between the Ig heavy chain and light chain gene breakpoints, an identity between BCL-1 and the PRAD1/cyclin D1 gene is strongly indicated.

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