ZIK1, A TRANSCRIPTIONAL REPRESSOR THAT INTERACTS WITH THE HETEROGENEOUS NUCLEAR RIBONUCLEOPROTEIN PARTICLE-K PROTEIN

The heterogeneous nuclear ribonucleoprotein particle (hnRNP) K protein is comprised of multiple modular domains that serve to engage a diver se group of molecular partners including DNA, RNA, the product of the proto-oncogene vav, and tyrosine and serine/threonine kinases. To iden tify additional K protein molecular partners and to further understand its function, we used a fragment of K protein as a bait in the yeast two-hybrid screen. The deduced primary structure of one of the positiv e clones revealed a novel zinc finger protein, hereby denoted as Zik1. In addition to the nine contiguous zinc fingers in the C terminus, Zi k1 contains a KRAB-A domain thought to be involved in transcriptional repression, Zik1 and K protein bound in vitro and co-immunoprecipitate d from cell extracts indicating that in vivo their interaction is dire ct. Expression of Gal4 DNA-binding domain-Zik1 fusion protein represse d a gene promoter bearing Gal4-binding elements, indicating that from cognate DNA elements Zik1 is a transcriptional repressor. The known di verse nature of K protein molecular interactions and now the identific ation of a K protein partner that is a transcriptional repressor lends support to the notion that K protein is a remarkably versatile molecu le that may be acting as a docking platform to facilitate communicatio n among molecules involved in signal transduction and gene expression.