We recently cloned a gene whose protein product binds to the Epstein-Barr virus BZLF1 gene promoter. The same gene has been previously cloned by another group who named it S mu bp-2 because its protein product binds to the S mu motif of the immunoglobulin heavy chain gene where it is postulated to function in immunoglobulin class switching. In the current study, we confirm that the S mu bp-2 gene is located on chromosome 11q13, a locus known to be altered by translocation in 50-70% of mantle cell lymphomas. We used Southern blot analysis to determine whether the S mu bp-2 gene was structurally rearranged in any of 25 mantle cell lymphomas. We found no evidence of rearrangement in any of these lymphomas including 18 that were proven to contain t(11;14) by cytogenetic analysis. These data suggest that structural alteration of the S mu bp-2 gene is not an underlying mechanism of tumorigenesis in mantle cell lymphomas.