ldhc expression in non-germ cell nuclei is repressed by NF-I binding

Developmental and testis-specific expression of the mouse lactate dehydroge nase C (mldhc) gene requires mechanisms for activation in germ cells and re pression in somatic cells. Promoter activity restricted to the testis has b een demonstrated using in vitro transcription assays with a 60-base pair pr omoter sequence upstream of the transcription initiation site. This promote r fragment has a TATA box and an overlapping 31-base pair palindromic seque nce. Here we have explored the role of the palindrome as a silencer of the ldhc gene in somatic tissues. A gel retardation assay detected two sites wi thin the palindrome that were important for protein binding. A member of th e NF-I/CTF family was identified as the protein binding to one of the sites . In transiently transfected mouse L cells, a promoter fragment in which th e NF-I site was mutated showed a 4-fold greater activity as compared with t he wild-type sequence. Overexpression of the four NF-I proteins, NF-IA, -B, -C, or -X, in mouse L cells transiently transfected with an ldhc promoter- reporter construct resulted in a 20-50% decrease in activity of the wild-ty pe promoter but had no effect when the NF-I binding element in the palindro me was mutated. These results indicate a role for the NF-I proteins in regu lation of the mldhc gene.