NUCLEAR-FACTOR-1 FAMILY PROTEINS BIND TO THE SILENCER ELEMENT IN THE RAT GLUTATHIONE TRANSFERASE-P GENE

We have previously identified a silencer region in the glutathione tra nsferase P (GST-P) gene, of which the expression is completely repress ed in liver of the rat. At least three traits-acting factors bind to m ultiple cis-elements in this region. Since GST-P silencer 4 (GPS4) is a dominant element in this silencer, we purified the GPS4 binding prot ein, called Silencer Factor A (SF-A). Purified SF-A was separated into several proteins on an SDS-polyacrylamide gel, and the amino acid seq uences of four major components of SF-A were determined. The amino aci d sequences of three fragments were identical to those of rat NF1-L, a nd that of the other fragment was the same as that of hamster NF1/Red1 . It is known that nuclear factor 1 (NF1) family proteins are encoded by at least four independent genes in vertebrates, and NF1-L and NF1/R ed1 are derived from different genes, NFI-A and NFI-B, respectively. T he microsequencing of SF-A revealed that at least two types of NF1 exi sted in rat liver. Functional analysis by using GAL4-fusion protein in HepG2 cells revealed that NFI-A repressed the transcription activitiy from human metallothionein IIA promoter. Our findings indicate that m ultiple forms of the NF1 family bind to the silencer region and contri bute to the negative regulation of the GST-P gene expression.