Phylogenetic Footprinting Reveals a Nuclear Protein Which Binds to Silencer Sequences in the Human y and e Globin Genes

• Published in: Molecular and cellular biology Vol. 12; no. 11; pp. 4919 - 4929
• Main Authors: Gumucio, Deborah L., Heilstedt-Williamson, Heidi, Gray, Todd A., Tarlé, Susan A., Shelton, David A., Tagle, Danilo A., Slightom, Jerry L., Goodman, Morris, Collins, Francis S.
• Format: Journal Article
• Language: English
• Published: Taylor & Francis 01-11-1992
• ISSN: 1098-5549; 1098-5549
• DOI: 10.1128/mcb.12.11.4919-4929.1992

Tissue- and developmental stage-specific expression of the human β-like globin genes is regulated by a combination of ubiquitous and erythroid-restricted trans factors that bind to cis elements near each of the five active genes. Additional interactions of these cis and trans factors with sequences located in the far 5' end of the cluster occur by as yet obscure mechanisms. Because of the complexity of this regulatory puzzle, precise identification of the determinants that control hemoglobin switching has proven difficult. Phylogenetic footprinting is an evolutionaiy approach to this problem which is based on the supposition that the basic mechanisms of switching are conserved throughout mammalian phylogeny. Alignment of the 5' flanking regions of the y genes of several species allows the identification of footprints of 100% conserved sequence. We have now tested oligomers spanning 13 such phylogenetic footprints and find that 12 are bound by nuclear proteins. One conserved element located at -1086 from the y genes exhibits repressor activity in transient transfection studies. The protein that binds this element, CSBP-1 (conserved sequence-binding protein 1), also binds at three sites within a silencer element upstream from the e globin gene. Further analysis reveals that the CSBP-1 binding activity is identical to that of a recently cloned zinc finger protein that has been shown to act as a repressor in other systems. The binding of CSPB-1 to silencer sequences in the e and y globin genes may be important in the stage-specific silencing of these genes.