SILENCER AND ENHANCER ELEMENTS LOCATED AT THE 3'-SIDE OF THE CHICKEN AND DUCK ALPHA-GLOBIN-ENCODING GENE DOMAINS

Enhancer activities have been observed in DNA fragments up to 1.36 kb long located on the 3'-side of the cluster of the three alpha-type glo bin-encoding genes in duck [Kretsovali et al., C.R. Acad. Sci. Paris 3 07 (1988) 563-568] and chicken [Knezetic and Felsenfeld, Mol. Cell. Bi ol. 9 (1989) 893-901]. We report here the identification of a chicken silencer element placed upstream from the three GATA-1 sites which con stitute the core enhancer element in both species. This silencer eleme nt can autonomously reduce the activity of promoters for thymidine kin ase and alpha(D) globin. Band shifts and DNase I footprinting experime nts using nuclear extracts from thermosensitive avian erythroblastosis virus-transformed chicken erythroblasts led to the delineation of thr ee sites for DNA-binding proteins within the silencer element.