Identification of a novel Ly49 promoter that is active in bone marrow and fetal thymus

The analysis of several Ly49 genes has identified a tissue-specific promoter adjacent to the previously defined first exon. The current study reveals the presence of an additional Ly49 promoter (Pro-1) and two noncoding exons upstream of the previously defined promoter (Pro-2). DNA sequences homologous to Pro-1 are present 4-10 kb upstream of Pro-2 in all Ly49 genes examined, and Pro-1 transcripts were detected from the Ly49a, e, g, o, and v genes. Pro-1 activity can be detected in bone marrow, embryonic thymus, freshly isolated liver NK cells, and the murine LNK cell line, but it does not function in adult thymus, sorted NK-T cells, spleen NK cells, or the EL-4 T cell line, even though these cells express Ly49 proteins. Luciferase reporter assays identified a Pro-1 core promoter region that functions in the LNK cell line but not EL-4 cells. The novel promoter is not active in mature NK cells, suggesting that Pro-1 represents an early Ly49 promoter.