Human fibroblast interferon RNA transcripts of different sizes in poly(I).poly(C) induced cells
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Abstract:
Northern blot analysis reveals that total RNA from human fibroblastoid cells (MG 63) induced with poly(I).poly(C) under conditions of IFN-beta production, contains predominantly a +/- 1,200 nucleotide long poly (A) mRNA (mRNA.M) which hybridizes with a Hu IFN-beta cDNA specific probe. But hybridization with this probe also enabled the detection of a polyadenylated RNA (RNA.I) with a length of between 3.5 kb-3.8 kb, representing 0.6% of the total hybridizable cellular RNA in superinduced cells. Mapping shows that the RNA.I contains all the sequence information present in mRNA.M. Furthermore, it also hybridizes to sequences, located downstream from the IFN-beta gene up to 2.5 kb beyond its poly A attachment site, while no hybridization to fragments located upstream of the IFN-beta mRNA cap site was observable. Hence this RNA.I corresponds to a transcript that starts at the same position as the major mRNA.M but which extends up to 2.5 kb beyond the 3'-end of mRNA.M where another polyadenylation signal is located.
Insights
Researchers identified a novel, extended transcript (RNA.I) of the human interferon-beta (IFN-beta) gene in fibroblastoid cells. This longer RNA molecule contains the full coding sequence of the standard IFN-beta mRNA but extends significantly beyond its polyadenylation site.
Area of Science:
- Molecular Biology
- Virology
- Immunology
Background:
- Interferon-beta (IFN-beta) is a crucial cytokine involved in antiviral and immune responses.
- Cellular responses to inducers like poly(I).poly(C) involve complex gene expression regulation.
Purpose of the Study:
- To characterize novel RNA species transcribed from the human IFN-beta gene.
- To investigate the full-length transcript structure and its relationship to the canonical IFN-beta mRNA.
Main Methods:
- Northern blot analysis was used to detect and size RNA transcripts.
- Hybridization with a human IFN-beta cDNA specific probe identified specific RNA sequences.
- RNA mapping experiments determined the extent and sequence content of the transcripts.
Main Results:
- A predominant polyadenylated mRNA (mRNA.M) of approximately 1,200 nucleotides was observed.
- A longer polyadenylated RNA (RNA.I), 3.5-3.8 kb, was detected, representing 0.6% of hybridizable RNA.
- RNA.I contains all sequences of mRNA.M and extends up to 2.5 kb downstream of the canonical polyadenylation site, indicating an alternative polyadenylation signal.
Conclusions:
- The human IFN-beta gene can produce an extended transcript (RNA.I) with an alternative, downstream polyadenylation site.
- This extended transcript shares the same transcription start site as the major mRNA.M.
- The discovery of RNA.I provides new insights into IFN-beta gene regulation and transcript diversity.