Lens-specific expression of the mouse αA-crystallin gene is regulated at the level of transcription. Here, we have studied the role of the PE1 region, which contains the TATA box (-31/-26) and the immediately adjacent PE1B sequence (-25/-12), in transcriptional regulation. Deletions within either the TATA box or PE1B sequence eliminated promoter activity in transfected lens cells. Surprisingly, these deletions did not eliminate lens-specific promoter activity of the transgene of transgenic mice. Transcription of the transgene with a TATA-deleted promoter Initiated at multiple sites in the lenses of the transgenic mice. Footprint analysis revealed that the entire PE1 region was protected by nuclear extracts prepared from lens cells which express the αA-crystallln gene and from fibroblasts which do not express the gene. The -37/+3 region formed three specific EMSA complexes using lens cell nuclear extracts, while a similar but much less intense pattern was observed when a fIbroblast nuclear extract was used. Competition experiments indicated that these complexes were not due to the binding of TBP to the TATA box, but rather to the binding of other nuclear proteins to the PE1B -25/-19 region. A series of co-transfectlon competition studies In vivo also suggested the functional Importance of proteins binding in the -25/-19 region. The PE1B proteln-DNA Interactions appear to be conserved in the chicken, rodent and human aA-crystallln gene as well as within the aA-and aB-crystallln genes In the mouse. Our findings indicate that the PE1B region is important for mouse αA-crystallin promoter activity; the proximity of this site to the TATA box raises the possibility for coopera-tivity or competition between TBP and PE1B-bound proteins.
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