A regulatory element in the 5'UTR directs cell-specific expression of the mouse alpha 4 gene

Transfection experiments showed that the mouse alpha 4 promoter contains a downstream element in its 5'UTR which is essential for efficient promoter activity. DNaseI footprinting and electrophoretic mobility shift assays (EMSA) demonstrated that the region from nt +113 to +148 can bind a cell type-specific factor (MIII-3) present in the alpha 4m expressing cell line L1210 but not in the non-expressing cell lines A9 and LMTK. Two consensus SP1 sites in this 5'UTR were recognised in L1210, A9 and LMTK, and with extracts from A9 and LMTK, an AP2-like protein was shown to bind a downstream AP2 site. Thus both ubiquitous and cell type-specific factors regulate the expression of alpha 4m.