Transcriptional regulation of murine beta1,4-galactosyltransferase in somatic cells. Analysis of a gene that serves both a housekeeping and a mammary gland-specific function.
beta1,4-Galactosyltransferase (beta4-GT) is a constitutively expressed enzyme that synthesizes the beta4-N-acetyllactosamine structure in glycoconjugates. In mammals, beta4-GT has been recruited for a second biosynthetic function, the production of lactose which occurs exclusively in the lactating mammary gland. In somatic tissues, the murine beta4-GT gene specifies two mRNAs of 4. 1 and 3.9 kilobases (kb), as a consequence of initiation at two different start sites approximately 200 base pairs apart. We have proposed that the region upstream of the 4.1-kb start site functions as a housekeeping promoter, while the region adjacent to the 3.9-kb start site functions primarily as a mammary gland-specific promoter (Harduin-Lepers, A., Shaper, J. H., and Shaper, N. L. (1993) J. Biol. Chem. 268, 14348-14359). Using DNase I footprinting and electrophoretic mobility shift assays, we show that the region immediately upstream of the 4.1-kb start site is occupied mainly by the ubiquitous factor Sp1. In contrast, the region adjacent to the 3.9-kb start site is bound by multiple proteins which include the tissue-restricted factor AP2, a mammary gland-specific form of CTF/NF1, Sp1, as well as a candidate negative regulatory factor that represses transcription from the 3.9-kb start site. These data experimentally support our conclusion that the 3.9-kb start site has been introduced into the mammalian beta4-GT gene to accommodate the recruited role of beta4-GT in lactose biosynthesis.
Rajput
B
B
Cell Structure and Function Laboratory, Oncology Center Department of Pharmacology and Molecular Sciences, School of Medicine, Johns Hopkins University, Baltimore, Maryland 21287-8937, USA.
Shaper
N L
NL
Shaper
J H
JH
D000818:Animals; D001483:Base Sequence; D002467:Cell Nucleus / Q000378:metabolism; D018983:DNA Footprinting; D003850:Deoxyribonuclease I; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D007739:L Cells; D007774:Lactation; D008321:Mammary Glands, Animal / Q000201:enzymology*; D051379:Mice; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009237:N-Acetyllactosamine Synthase / Q000096:biosynthesis* / Q000235:genetics*; D009838:Oligodeoxyribonucleotides; D009928:Organ Specificity; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000096:biosynthesis / Q000302:isolation & purification; D012045:Regulatory Sequences, Nucleic Acid; D015183:Restriction Mapping; D016329:Sp1 Transcription Factor / Q000378:metabolism; D015534:Trans-Activators / Q000302:isolation & purification / Q000378:metabolism; D014157:Transcription Factors / Q000302:isolation & purification / Q000378:metabolism*; D014158:Transcription, Genetic
D009838:Oligodeoxyribonucleotides; D012333:RNA, Messenger; D016329:Sp1 Transcription Factor; D015534:Trans-Activators; D014157:Transcription Factors; D009237:N-Acetyllactosamine Synthase; D003850:Deoxyribonuclease I