Transcription Termination/Polyadenylation Occurs at Multiple Sites in the Human Type I Interferon Receptor Gene

Based on the previously reported sequence, we isolated an independent cDNA clone encoding a binding component of the human type I interferon receptor (IFN-R). This cDNA is identical to the published sequence except that it lacks 62 bases of 5′ untranslated sequence and terminates at the first of two potential polyadenylation sites. In Northern blot analyses of poly(A)⁺RNAs from both IFN-sensitive and IFN-resistant Daudi cells, this cloned cDNA hybridized to a predominant mRNA of 2.4 kb, as well as to mRNAs of 1.8, 4.8, and 5.6 kb, and occasionally 6.9 kb. These various transcripts, which were also observed at similar levels in Raji B cells and two T-cell lines, Jurkat and MOLT-4, were detected after high-stringency washes, and by alternate probes corresponding to subfragments of the cDNA. In contrast, only the 4.8- and 5.6-kb transcripts hybridized to a polymerase chain reaction (PCR)-derived probe that corresponded to genomic sequences immediately down-stream from the second polyadenylation site. These results indicate that the latter transcripts arise from the same gene as the predominant 2.4-kb mRNA due to incomplete transcription termination at either of the known polyadenylation sites. Finally, Northern blot analysis of total RNAs revealed the presence of the predominant 2.4-kb type I IFN-R transcript in numerous tissues from second trimester human fetuses, suggesting that the type I IFN-R gene is constitutively expressed in multiple cell types.