DNA binding factors which interact with the Sp1 site of the chicken δ1-crystallin promoter are developmentally regulated

Abstract

Transcription of the δ1-crystallin gene is developmentally regulated in the embryonic chicken lens. Previous work defined a positive transcription regulatory element between positions −120 and −43 of the δ1-crystallin promoter. This region contains a putative Sp1 binding site (−78 to −71), adjacent to a CAAT box (−70 to −67). Gel retardation assays using lens nuclear extracts revealed two protein-DNA complexes which involved the Sp1 site. The formation of the complexes increased from day 6 to day 11 of embryogenesis (period of lens orgenogenesis) peaked between days 11 and 15, then decreased in a non-parallel manner until hatching (day 21). A point mutation in the Sp1 binding site of the δ1-crystallin promoter abolished formation of one of the complexes (complex 1, slower in mobility), while point mutations in the CAAT box had no effect on the formation of either complex. Studies using purified Sp1 protein and increasing amounts of embryonic chicken lens nuclear extracts showed cooperativity in the formation of both complexes, more remarkable with complex 1.