Purification and cloning of type A/B hnRNP proteins involved in transcriptional activation from the rat spi 2 gene GAGA box

The GAGA box of the rat serine protease inhibitor 2 (spi 2) genes not only acts as a basal promoter element, but also mediates transcriptional activat ion by growth hormone and interleukin-6. The GAGA box is separated from the TATA box by only 12 bp, and this close association is required for efficie nt transcription. Hence, the GAGA box may influence transcription efficienc y through interactions between GAGA box binding proteins and some component s of the RNA polymerase II complex. Here we report the cloning of two GAGA box-binding proteins termed p38 and p40, that belong to the type A/B hetero geneous nuclear ribonucleoprotein subgroup. GAGA box mutations that diminis h the affinity for p38 and p40 decrease basal and GH-induced reporter gene expression. Furthermore, nuclear extracts depleted of p38 and p40 can no lo nger support GAGA box-dependent in vitro transcription. Therefore, two poly peptides previously assigned to a family of RNA processing proteins also ac t as DNA-binding, promoter-specific transcription factors.