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Abstract
PURPOSE: To delineate cis-acting DNA elements involved in the expression of the human red and green visual pigment genes and to correlate these with transcription factor binding sites. METHODS: Assays of promoter activity were accomplished by transient transfection into WERI cells. Nested deletion and block mutagenesis were undertaken to delineate critical elements. Transcription factor binding sites were determined by DNase I footprinting and electrophoretic mobility shift (EMSA) analyses. RESULTS: The human retinoblastoma cell line WERI, but not Y-79, was found to express the red and green pigment genes. Transfection assays in WERI cells revealed that the proximal region of the red pigment gene promoter had positive (-130 to -113 and -96 to -23) and negative (-190 to -130 and - 113 to -96) regulatory elements. The green pigment gene promoter was found to be 2 to 4 times more active than was that of the red pigment. This difference in activity was attributable mainly to a T to C substitution at position -3. DNase I protection and EMSA studies demonstrated the binding of several ubiquitous and WERI-enriched proteins to DNA sequences between - 130 and the TATA box. The locus control region (LCR) did not have any enhancer activity in transient transfection. CONCLUSIONS: The WERI cell line is a good model system for the analysis of gene expression of the human cone visual pigment genes. The expression of these genes in a cell-specific fashion seems to be controlled mainly by positive-acting elements in the region between - 130 and the TATA box. The higher activity of the green pigment gene promoter could have evolved to compensate for its longer distance from the activating LCR than that of the red pigment gene promoter (approximately 34 versus 3.5 kb). Although the LCR does not enhance transcription in transient transfection, it binds factors that also recognize the proximal promoter region. These interactions may be important for the establishment of a transcriptionally active domain in a chromatin context.