The RCK/P54 gene was previously isolated from the chromosome translocation breakpoint region on 11q23 of a human lymphoma cell line, RC-K8, with t(11;14)(q23;q32). It was found to encode a 472-483-amino-acid (aa) polypeptide belonging to an RNA helicase/translation initiation factor family. The aim of the present investigation was the isolation and comparative sequence analysis of the mouse RCK/P54 cDNA from a BALB/c spleen cDNA library. Sequence analysis revealed an open reading frame (ORF) predicting a polypeptide of 483 aa showing 97.7% identity to human RCK/p54. Northern analysis demonstrated a 7.5-kb signal in all tissues tested and in vitro translation analysis showed a 54-kDa polypeptide. These results indicate that both mouse and human RCK/P54 are highly conserved.