Capturing nuclear sequence-specific DNA-binding proteins by using simian virus 40-derived minichromosomes

A pancreatic exocrine cell factor and AP4 bind overlapping sites in the amylase 2A enhancer

A factor found in pancreatic exocrine cell lines and pancreatic nuclei binds selectively to the alpha-amylase 2A transcriptional enhancer. Pancreatic exocrine cell extracts protect asymmetrically an unusually large, 35 base pair region from DNase I digestion in vitro, suggesting the involvement of a multimeric DNA binding complex. We show that this region of the enhancer contains a major affinity recognition sequence for the HeLa transcription factor AP4. A 4 base pair mutation in the enhancer sequence shown previously to abolish activity in vivo [Boulet, A. M., Erwin, C. R., & Rutter, W. J. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 3599-3603] abolishes AP4 binding in vitro and weakens but does not eliminate the binding of adjacent enhancer factors. Further, sequences similar to the AP4 binding site are found within a consensus sequence of most pancreatic exocrine genes (Boulet et al., 1986). We have identified three AP4 binding sites in the pancreatic elastase gene: one occurs in the consensus sequence of the enhancer. Thus, protein(s) with the binding selectivity of AP4 may play a role in the expression of the pancreatic exocrine gene family.

Unidirectional deletion and linker scan analysis of the late promoter of the human papovavirus BK

We have previously shown that the late promoter of the human papovavirus BK (prototype) is contained within the three 68-bp repeats and a 66-bp region to the late side of the repeats which together constitute the early promoter enhancer. We have now carried out unidirectional deletion and linker scan analyses of these sequences to identify the major elements of the late promoter in human and monkey cells. Several important sequence motifs involved in late promoter function are found throughout this region. The most active ones correspond to previously defined binding sites for the transcription factors NF1 and Sp1 and a GC-rich region known to be important for early promoter function. The NF1 sequences may also be involved in negative regulation in some situations.