Tissue-specific factors and glucocorticoid receptors present in nuclear extracts bind next to each other in the promoter region of mouse mammary tumor virus

Nuclear extracts from different mouse tissues have been used to study the interaction of factors with the steroid-inducible promoter of mouse mammary tumor virus. In addition to the glucocorticoid receptor that interacts with the distal region of the promoter, several tissue-specific proteins were found to bind to the 5' flanking region of the receptor-binding site and to the basal promoter region. The differences in the pattern of protection observed suggest that tissue-specific factors might co-operate with steroid receptors and result in a cell-type-dependent modulation of hormone action.     

Plant nuclear factor ASF-1 binds to an essential region of the nopaline synthase promoter

We have characterized a tobacco nuclear factor that binds to the -118 region of the nopaline synthase (nos) promoter from the Ti plasmid of Agrobacterium tumefaciens. The binding site for this factor, identified by DNase I footprinting, encompasses the region from -138 to -103 of the nos promoter. This region, which contains a potential Z-DNA-forming sequence, was previously shown to be essential for nos promoter activity in transgenic tobacco. A synthetic 21-base pair sequence from the protected region (from -131 to -111), designated as nos-1, was sufficient for factor recognition in vitro. In transgenic tobacco, a tetramer of nos-1 can confer leaf and root expression when fused upstream of a truncated 35 S promoter from the cauliflower mosaic virus. Mutations at the two TGACG-like motifs in nos-1 abolish factor binding while preserving the potential for Z-DNA formation. A tetramer of the nos-1 mutant sequence has no significant activity above background when tested in transgenic tobacco. Competition experiments with activation sequence factor (ASF)-1 binding sites from the 35 S promoter of cauliflower mosaic virus (as-1) and the wheat histone H3 promoter (hex-1) demonstrate that ASF-1 is the factor that binds to nos-1.     

Age-related binding of proximal region of ApoE promoter to nuclear proteins of mouse cerebral cortex

Mouse ApolipoproteinE (ApoE) gene has maximum promoter activity in the proximal region (−212 to +54) which includes different regulatory elements. These elements bind to specific protein factors and influence the expression of genes which are involved in key brain functions that decline with age. As there is no information on the binding of apoE promoter to nuclear proteins as a function of age, we have analyzed the binding of USF, AP1 and one negative element sequence present in ApoE proximal promoter to nuclear proteins of the cerebral cortex of mice of different ages. The findings show the formation of one complex with USF and two complexes with AP1 and negative element. The intensity of these complexes varies with age, indicating differential binding of protein factors to specific elements of apoE promoter, which reflect age-related regulation of apoE -mediated brain functions.