The cDNA insert of the plasmid p14-6 is found to be the 3'-untranslated region (3'-UTR) of the transcription factor for human interleukin-6, NF-IL6. This 3'-UTR is actively transcribed in the revertant cell line RR, which contains the p14-6 plasmid integrated into its genomic DNA. Simultaneously a protein specifically bound to this 3'-UTR is expressed in significantly larger amounts. Its overexpression is apparently related to the reversion of the malignant cellular phenotype. The properties of this protein, named BNF, and possible reasons for its overexpression are discussed, and hypothesis on the mechanism of reversion of the RR cells is proposed.