A novel human gene, named E9730 (a clone number of fetal liver cDNA library), has been identified from more than 14,000 expressed sequence tags (ESTs) based on our large scale sequencing of human fetal liver cDNA libraries. Although sequencing of this novel human gene indicates that it is a leucine zipper protein, the function of E9730 and its homologous genes among species is unknown yet. To find out physiological functional clue of E9730, the yeast two-hybrid system was used to screen the E9730-interac- ting protein(s), and one clone containing a cDNA insert with almost the entire coding sequence (amino acids 39-335) of human Jab1 (Jun-activating domain binding protein 1) that interacted specifically with E9730 was identified. A specific association between Jab1 and E9730 was shown by co-immunoprecipitation and co-localization experiments. Furthermore, E9730 appeared to enhance Jab1-induced AP-1 activity in a con- centration-dependent manner and Jab1 may be involved in the intracellular signaling transduction from E9730 to AP-1.
