Nucleotide sequence of the third cytokine LD78 gene and mapping of all three LD78 gene loci to human chromosome 17.

Cytokine LD78 is a member of a newly identified cytokine superfamily. We cloned the third human gene for the LD78, termed LD78 gamma and the sequence analysis showed that it is a 5'-truncated pseudogene. Exons 2 and 3 and the intron between them are highly homologous to those of the LD78 beta gene, hence, the gamma gene was probably derived from the beta gene. Southern blot analysis of human x mouse somatic hybrid cell DNAs and in situ hybridization experiments mapped all the three gene loci on human chromosome 17q21.1-q21.3. Analysis of DNAs from family members supports our previous finding that the beta and gamma genes on each of the paired chromosome 17 vary in copy number and that the LD78 alpha gene is presumably a single copy. In our analyses of cosmid clones, the LD78 beta gene and the second gene for AT744, which is also a member of the superfamily are closely linked in a head-to-head arrangement. The mechanism of generation of the three LD78 genes is discussed.