Bop: a new T-cell-restricted gene located upstream of and opposite to mouse CD8b

In the course of transient expression studies undertaken to determine the location of the mouse CD8b gene promoter, two additional promoter activities were detected within 600 nucleotides upstream of the gene. One activity directs transcription in the same direction as CD8b but fails to transcribe the CAT reporter gene due to an apparent transcription-blocking element lying between it and the gene. The second activity directs transcription opposite to that of the CD8b gene. Northern hybridization with a probe consisting of nucleotides -875 to -550 relative to the site of CD8b transcription initiation revealed hybridizing species of 4 kilobases (kb) and 1.8 kb in poly-A-selected RNA from mouse thymus but not from any other tissues. Similar RNA species were detected in poly-A+ RNA from concanavalin A-stimulated spleen cells and several long-term CTL lines but not from the EL4 or BW5147 T-cell lines or the J558L myeloma. The mRNA species were most abundant in cells of a secondary mixed leukocyte culture which were greater than 95% CD8(+). Northern hybridizations using single-stranded unidirectional probes indicated that these mRNAs represent transcription opposite to the CD8b gene. The tissue and cell type distribution of this newly-discovered gene (designated Bop for CD8b opposite) are consistent with T-cell-specific and possibly CD8-positive T-cell-specific expression. The head-to-head arrangement of the Bop and CD8b genes is reminiscent of the arrangement of the Tap1 and Lmp2 genes, and the expression of the Bop gene in CD8-positive cells raises the possibility that these genes are involved in the same functional pathway.