Expression of the RCK gene, which is a target gene on 11q23 of the t(11;14) (q23;q32) translocation in the B-cell lymphoma cell line RC-K8, was studied by Northern and Western blot analyses. The RCK gene product is a member of the D-E-A-D box protein/RNA helicase family. With the use of Northern blot analysis, a 7.5-kb transcript of the RCK gene was shown to be expressed ubiquitously in human and mouse tissues. Polyclonal antibodies against the RCK gene product were raised, and the RCK gene expression pattern was examined in human and mouse tissues. Two different polyclonal anti-rck antibodies detected a specific 54-kilodalton product named rck/p54 in the majority of human and mouse tissues tested by Western blot analysis. However, rck/p54 was shown to be very low in the human brain and was not detectable in lumbar muscle and lung tissues, although RCK mRNA is abundantly present in these tissues. It is of interest that malignant transformed human cells arising from tissues with low or no expression of rck/p54, such as neuroblastoma, glioblastoma, rhabdomyosarcoma, and lung cancer cell lines, produced a moderate amount of rck/p54 protein, suggesting that rck/p54 plays a role in tumorigenesis. In addition, the rck/p54 protein was localized to cytoplasm by immunostaining with the use of laser microscopy and by subcellular fractionation.