SPRUNT-1, A NEW MEMBER OF THE RUNT DOMAIN FAMILY OF TRANSCRIPTION FACTORS, IS A POSITIVE REGULATOR OF THE ABORAL ECTODERM-SPECIFIE CYIIIA GENE IN SEA-URCHIN EMBRYOS

In this paper we present a structural and functional characterization of a new sea urchin embryo transcription factor, SpRunt-1. This factor was isolated by means of its specific interaction with a cis-regulato ry target site of the CyIIIa gene. Here we show that this target site, the P7I site, is required for normal embryonic activation of CyIIIa . CAT reporter gene constructs. An oligonucleotide affinity column bear ing the P7I target site purifies a 21-kDa polypeptide from blastula-st age nuclear extracts, and the amino acid sequence obtained from this p olypeptide was used to generate a nucleic acid probe with which the co rresponding cDNA was cloned. The cDNA encodes an approximately 60-kDa protein, SpRunt-1, which includes a ''runt domain'' that is closely ho mologous to those of Drosophila and mammalian runt domain transcriptio n factors. RNA and genomic blots show that SpRunt-1 is represented by a single embryonic transcript, encoded by one of possibly two runt-dom ain-containing genes. By RNA probe protection we found that transcript s of SpRunt-1 increase in concentration dramatically after the blastul a stage of development, suggesting that the up-regulation of CyIIIa th at occurs after blastula stage is a function of zygotically transcribe d SpRunt-1. These results are discussed with reference to known featur es of the runt domain family of transcription factors. (C) 1996 Academ ic Press, Inc.