THE GENE FOR HISTONE RNA HAIRPIN BINDING-PROTEIN IS LOCATED ON HUMAN-CHROMOSOME-4 AND ENCODES A NOVEL TYPE OF RNA-BINDING PROTEIN

The hairpin structure at the 3' end of animal histone mRNAs controls h istone RNA 3' processing, nucleocytoplasmic transport, translation and stability of histone mRNA. Functionally overlapping, if not identical , proteins binding to the histone RNA hairpin have been identified in nuclear and polysomal extracts. Our own results indicated that these h airpin binding proteins (HBPs) bind their target RNA as monomers and t hat the resulting ribonucleoprotein complexes are extremely stable. Th ese features prompted us to select for HBP-encoding human cDNAs by RNA -mediated three-hybrid selection in Saccharomyces cerevesiae. Whole ce ll extract from one selected clone contained a Gal4 fusion protein tha t interacted with histone hairpin RNA in a sequence- and structure-spe cific manner similar to a fraction enriched for bovine HBP, indicating that the cDNA encoded HBP. DNA sequence analysis revealed that the co ding sequence did not contain any known RNA binding motifs. The HBP ge ne is composed of eight exons covering 19.5 kb on the short arm of chr omosome 4. Translation of the HBP open reading frame in vitro produced a 43 kDa protein with RNA binding specificity identical to murine or bovine HBP. In addition, recombinant HBP expressed in S.cerevisiae was functional in histone pre-mRNA processing, confirming that we have in deed identified the human HBP gene.