Human fibroblast but not lymphoid cells have unusually long polyadenylated interferon-beta 1 mRNAs.

The transcription unit of human interferon-beta 1 (IFN-beta 1) mRNA was examined by chain elongation of nascent RNA in isolated nuclei of human fibroblasts and lymphoid cells induced to produce IFN. In fibroblasts, transcription proceeds beyond 2,400 nucleotides downstream from the poly(A) site of mature mRNA and appears to terminate in the region rich in Alu sequences. Northern hybridization showed the presence of a minor polyadenylated RNA species, about 3,200 nucleotides long, that hybridized to the probes derived from 3'-flanking regions of IFN-beta 1 mRNA. S1 nuclease analysis established that this long polyadenylated transcript represents a mixture of three RNA molecules with defined 3' termini. In all three mRNAs, as in mature IFN-beta 1 mRNA, the polyadenylation site was located within a few nucleotides downstream from the AAUAAA hexanucleotide consensus sequence. Surprisingly, in Namalva lymphoblastoid cells no transcription beyond the polyadenylation site of mature IFN-beta 1 mRNA could be detected either in isolated nuclei or total RNA.