alpha B-crystallin TATA sequence mutations: lens-preference for the proximal TATA box and the distal TATA-like...

The mouse alpha B-crystallin promoter is active in lens (preferentially), heart and skeletal muscle, and contains a proximal (-28/-22) and distal (-76/-69) TATA sequence. The present investigation explores by site-specific mutagenesis of alpha B-crystallin promoter-chloramphenicol acetyltransferase (cat) reporter gene constructs the function of these two potential TATA boxes in transfected lens cells and transgenic mice. Unexpectedly, mutagenesis of either or both TATA sequences had no effect on promoter activity in transfected lens cells. By contrast, in transgenic mice mutagenesis of the proximal, distal or both TATA sequences preferentially reduced promoter activity in the lens, with minimal effect in the heart or muscle. 5' RACE analysis of lens and muscle RNA of transgenic mice showed that elimination of the proximal TATA box led to transcription initiation at position -48. This upstream initiation site was apparently not due to the utilization of the distal TATA sequence, since the transgene carrying mutations in both TATA sequences also initiated at position -48. The preferential function of the distal TATA sequence in the lens is probably due to the binding of a transcription factor unrelated to transcription initiation, while the preferential lens function of the proximal TATA box appears to involve transcription initiation.