Transacting Nuclear Proteins That Bind to the Upstream Regulatory Region of a MHC Class I Gene

Abstract

Expression of MHC class I gene is regulated via the highly conserved 5’ class I regulatory element (CRE) and interferon consensus sequence (ICS). The CRE exerts both negative and positive regulation that is responsible for developmental control of the MHC class I gene expression. The ICS is involved in elevating transcription of MHC class I gene in response to interferon treatment. We examined the presence of transacting nuclear factors which interact with these regulatory sequences in a variety of cells. In gel mobility shift analyses we show that in cells expressing MHC class I genes possess at least three distinct nuclear factors capable of binding to the CRE. These three nuclear factors bind DNA sequences comprizing precise direct- and inverted repeats within the CRE. F9 embryonal carcinoma cells lack one of the three factors, which may be relevant to the absence of MHC gene expression in these cells. We also show that the ICS binds a unique nuclear factor, independent of the above factors. Tests with a number of mutant duplex oligonucleotides allowed us to localize the binding site of the factor to the core region of the ICS.