THE SILENCER OF MOUSE PGK-2 CONSISTS OF 2 DISCRETE DNA ELEMENTS THAT INDIVIDUALLY HAVE NO EFFECT

Pgk-2 encodes a testis-specific phosphoglycerate kinase isozyme (PGK), and the expression of mouse Pgk-2 is activated during the spermatogen ic pathway at the pachytene spermatocyte stage. We previously reported the identification of a silencer-like cis-acting element in a region between nucleotides (nt) - 1404 and - 685 of mouse Pgk-2, which could be responsible for the repression of Pgk-2 expression in somatic tissu es and pre-meiotic testicular germ cells. In the present study, the si lencer was precisely located within an 87-bp region between nt -882 an d -796. This region contained two distinct sequences that individually bound factors present in nuclear extracts of mouse cultured cells and rat tissues. The two sequences, when aligned in tandem upstream from the Pgk-2 promoter, inhibited cat expression driven by the promoter in mouse erythroleukemia cells, whereas either sequence alone did not sh ow any effect. The results indicate that the Pgk-2 silencer consists o f two distinct DNA elements which do not individually influence promot er activity. Binding of distinct nuclear factors to each DNA element a ppeared to be required for the silencer action.