RP105 is a mouse B cell surface molecule that transmits a growth- promoting signal and is implicated in the life/death decision of B cells. RP105 has tandem repeats of a leucine-rich motif in the extracellular domain that is expected to be involved in protein-protein interactions. In the present study, a cDNA clone encoding the human homologue of RP105 was isolated. The amino acid sequence of human RP105 is highly homologous to that of mouse RP105 with 74% identity, and the leucine-rich repeats are well conserved. The expression of the human RP105 transcript was detected in some B cell lines, a histiocytic leukemia cell line, and peripheral blood leukocytes. We also determined the chromosomal locations of the mouse RP105 gene (Ly64 locus) and the human RP105 gene (LY64 locus). Interspecific mouse backcross analysis was used to map the Ly64 locus at the distal region of chromosome 13. The human LY64 locus was localized to 5q12 by fluorescence in situ hybridization, confirming the syntenic relationship between these regions of the mouse and human chromosomes.
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