Evidence for positive and negative regulation in the promoter of the chicken δ1-crystallin gene

We investigated the role of sequences flanking the transcription initiation site of the δ1-crystallin gene in transient transfection assays of primary embryonic chicken lens epithelial cells or fibroblasts. Varying lengths of the 5′ flanking sequence of the δ1-crystallin gene (containing some untranslated sequence from exon 1) were fused to the bacterial chloramphenicol acetyltransferase (CAT) gene in the pSVOCAT plasmid. A plasmid carrying the bacterial β-galactosidase gene driven by the Rous sarcoma virus (RSV) promoter was used as an internal control. Standardized results showed that the sequence located between -120 to -43 exhibited strong promoter activity; however, the promoter activity was markedly reduced (20-fold) when the upstream sequence between -603 and -120 was included in the construct. The δ1-crystallin promoter displayed little lens preference. This upstream sequence did not reduce the activity of the Simian virus 40 (SV40) early promoter (with or without its enhancer) or the Herpes thymidine kinase promoter in transfection tests, indicating some specificity in its effect. Evidence for a δ1-crystallin negative trans-acting factor was provided by competition experiments. Our data raise the possibility that expression of the δ1-crystallin gene involves a negative cis-acting transcription element, a speculation which may deserve further attention in view of the gradual decrease in δ-crystallin synthesis in the developing lens.