The 3'UTR of eukaryotic mRNA is an important regulation region, on which many trans factors act. In recent years, a series of 3'UTRs were shown, to have tumor suppressor function, including the 3'UTR of the human nuclear factor for interleukin-6 (NF-IL6 3'UTR). To understand molecular basis for this function, we have tried to isolate genes encoding protein factors acting on the RNA of NF-IL6 3'UTR. Here we show that, by using a yeast three-hybrid system, a cDNA fragment was successfully isolated. This cDNA was allowed to express in E. coli, and its expression product, a polypeptide of ca. 70 amino acids long, was shown to specifically bind to the NF-IL6 3'UTR RNA. A search in GenBank did not reveal homologous sequences. Therefore, this cDNA fragment may be a part of the gene of a novel NF-IL6 3'UTR specific binding protein.