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Site-specific cleavage of IGF-II mRNAs requires sequence elements from two distinct regions of the IGF-II gene
D Meinsma1, W Scheper, P E Holthuizen
1Wilhelmina Childrens' Hospital, State University of Utrecht, The Netherlands.
Abstract:
The human insulin-like growth factor II (IGF-II) gene constitutes a complex transcriptional unit that contains nine exons and four promoters. Expression of the IGF-II gene yields a family of mRNAs that all encode prepro-IGF-II. In addition, a stable 1.8 kb RNA is formed that is derived from the 3' untranslated region of exon 9. Recently, we have shown that this RNA species arises by site-specific endonucleolytic cleavage of IGF-II mRNAs and not by transcription from a separate promoter. In the present study we establish that two widely separated sequence elements of approximately 300 nucleotides, both located within exon 9, are required for this cleavage reaction. The first element encompasses about 200 nucleotides upstream and 100 nucleotides downstream of the cleavage site, while the second element is located within a region of 330 nucleotides about 2 kb upstream of the cleavage site. Interestingly, site-specific cleavage also occurred when a fragment from exon 9 of the IGF-II gene containing these two elements was inserted into the 3' untranslated part of the beta-globin gene. Apparently, the expressed hybrid beta-globin-IGF-II mRNA contains all the regulatory elements to confer site-specific endonucleolytic cleavage.
Insights
Two sequence elements within exon 9 of the human insulin-like growth factor II (IGF-II) gene are essential for site-specific endonucleolytic cleavage. This process generates a stable 1.8 kb RNA from IGF-II mRNAs.
Area of Science:
- Molecular Biology
- Gene Regulation
- RNA Processing
Background:
- The human insulin-like growth factor II (IGF-II) gene is a complex transcriptional unit.
- IGF-II gene expression produces multiple mRNAs encoding prepro-IGF-II and a distinct 1.8 kb RNA derived from exon 9's 3' untranslated region.
Purpose of the Study:
- To identify the specific sequence elements within the IGF-II gene responsible for the site-specific endonucleolytic cleavage of its mRNAs.
- To investigate the regulatory mechanisms governing the generation of the stable 1.8 kb RNA from IGF-II transcripts.
Main Methods:
- Analysis of sequence elements within exon 9 of the IGF-II gene.
- Site-directed mutagenesis and RNA cleavage assays.
- Gene construct insertion into the beta-globin gene to assess regulatory element function.
Main Results:
- Two distinct sequence elements, located within exon 9 and approximately 2 kb apart, are crucial for the endonucleolytic cleavage reaction.
- The first element spans approximately 300 nucleotides around the cleavage site, and the second is located 2 kb upstream.
- Functional regulatory elements were confirmed when inserted into the beta-globin gene, enabling site-specific cleavage of the hybrid mRNA.
Conclusions:
- The site-specific cleavage of IGF-II mRNAs is mediated by two specific sequence elements within exon 9.
- These elements contain the necessary regulatory information to direct endonucleolytic processing, independent of their original genomic context.
- This finding elucidates a novel mechanism for generating specific RNA species from complex gene loci.