Developmental appearance of transcription factors that regulate liver-specific expression of the aldolase B gene.

The region from -202 to -1 of the rat aldolase B (AldB) promoter directs tissue-specific transcription in vitro. Deletion of the half of this promoter distal to its origin reduced its ability for tissue-specific expression. Two protein-binding sites in this distal element have been identified and characterized. One bound a factor named AIF-A, which is probably identical to previously characterized liver-specific factors HNF-1 and APF. The other, containing a CCAAT motif, bound a factor named AIF-B. These two factors were considerably enriched in liver cells compared with other cells not expressing AldB. In the liver, these two factors increased prior to the activation of the AldB gene during development. Liver-specific in vitro transcription assays indicated that the binding of both factors to their target sequences was required for AldB transcription. These results suggest that AIF-A and AIF-B are positively acting transcription factors that regulate tissue-specific and development stage-specific activation of the AldB gene.