Mapping of the transcriptional regulatory domains responsible for the difference in the promoter activity between mouse C4 and Slp (sex-limited protein) genes.

The genes for the fourth complement component (C4) and sex-limited protein (Slp) of the mouse exhibit a high degree of sequence homology and have probably been derived by recent gene duplication from a common ancestor gene, but their mode of expression is greatly different in most standard mouse strains. Although the C4 gene is constitutively expressed, the Slp gene is expressed only under the influence of androgens or not expressed at all. To map the transcriptional regulatory domains that are responsible for the difference in the promoter activity between the mouse C4 and Slp genes, we constructed various hybrid promoters from the 5'-flanking DNA of the C4 and Slp genes of the FM strain and tested for their transcriptional activity. The hybrid promoters were inserted into the HindIII site located immediately upstream of the chloramphenicol acetyl transferase (CAT) gene of the plasmid pSVOcat. The expression of CAT was assayed in transiently transfected HepG2 cells and in permanently transfected Ltk- cells. The transcriptional regulatory region responsible for the difference between the C4 and Slp gene expression was mapped within the 5'-flanking region of about 400 nucleotides near the promoters of the C4 and Slp genes. By S1 mapping analysis, it was shown that the CAT activities expressed in transfected cells were due to the transcripts correctly initiated from the promoter of the C4 or Slp genes in the chimeric constructs.