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Unusually long mRNA species coding for human alpha and beta interferons
Abstract:
Each of the several intronless interferon (IFN) alpha S genes is embedded in 4- to 5-kilobase (kb) DNA homology units which are arranged more or less in tandem in the human genome. In addition to the expected 0.8- to 1.4-kb-long IFN-alpha S mRNA species, we have detected polyadenylylated RNA molecules approximately 2-2.7, 3.5-4.5, and 7-8 kb long derived from IFN-alpha S genes in the cytoplasm of Sendai virus-induced bromodeoxyuridine-treated human lymphoblastoid (Namalwa) cells. These transcripts were detected by electrophoresis of cytoplasmic polyadenylylated RNA through agarose-CH3HgOH gels followed by blothybridization using an IFN-alpha 1 (a prototype alpha S) cDNA probe and also by translation of the eluted RNA into biologically active IFN in the Xenopus oocyte assay. At least some of these long translationally active RNA molecules appear to represent functional mRNA species because they can be detected in polysomes. In addition, the oocyte translation assay has revealed the presence of unusually long (2-8 kb) IFN-beta mRNA species both in Sendai virus-induced Namalwa cells and in poly(I) . poly(C)-induced diploid human fibroblasts (FS-4). The detection of very long IFN-alpha 1-related mRNA species suggests that some of the DNA sequence features observed in the flanking homology units may affect the transcription of the IFN-alpha S genes. Our hybridization analyses also indicate that the 1.8-kb human IFN-alpha L mRNA(s) shows no detectable cross-hybridization with an IFN-alpha 1 cDNA probe. Thus, this mRNA is derived from a gene(s) that is distinct from the IFN-alpha S set.
Insights
Researchers found longer interferon (IFN) alpha S and IFN-beta mRNA species in human cells. These longer transcripts are functional and suggest genomic DNA structures influence interferon gene transcription.
Area of Science:
- Molecular Biology
- Immunology
- Genetics
Background:
- Interferon (IFN) alpha S genes are intronless and located within DNA homology units in the human genome.
- Standard IFN-alpha S mRNA species are typically 0.8-1.4 kb.
Purpose of the Study:
- To investigate the full spectrum of RNA transcripts derived from IFN-alpha S genes.
- To determine the functional relevance of detected RNA transcripts.
- To explore potential regulatory mechanisms influencing interferon gene expression.
Main Methods:
- Detection of polyadenylylated RNA using Northern blot hybridization with an IFN-alpha 1 cDNA probe.
- Analysis of RNA transcripts in the cytoplasm of human lymphoblastoid (Namalwa) cells and diploid human fibroblasts (FS-4).
- Assessment of RNA translational activity using the Xenopus oocyte assay and polysome analysis.
Main Results:
- Identification of unexpectedly long polyadenylylated RNA molecules (2-8 kb) derived from IFN-alpha S genes in Namalwa cells.
- Demonstration that these long transcripts are translationally active and present in polysomes, indicating functional mRNA.
- Detection of similarly long IFN-beta mRNA species in both Namalwa and FS-4 cells.
- Observation that IFN-alpha L mRNA does not cross-hybridize with IFN-alpha 1 cDNA, suggesting it originates from a distinct gene set.
Conclusions:
- The human genome contains and expresses unusually long IFN-alpha S and IFN-beta mRNA species.
- These long transcripts are functional and may be influenced by DNA sequence features in flanking homology units.
- IFN-alpha L mRNA represents a distinct transcript class separate from the IFN-alpha S gene family.