Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.7.49 (reverse transcriptase)
 31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The first step in the splicing of an intron from nuclear precursors of mRNA results in the formation of a lariat structure. A distinct intronic nucleotide sequence, known as the branchpoint region, plays a central role in this process. We here describe a point mutation in such a sequence. Three sisters were shown to suffer from fish-eye disease (FED), a disorder which is caused by mutations in the gene coding for lecithin:cholesterol acyltransferase (LCAT). Sequencing of the LCAT gene of all three probands revealed compound heterozygosity for a missense mutation in exon 4 which is reported to underlie the FED phenotype, and a point mutation located in intron 4 (IVS4:T-22C). By performing in vitro expression of LCAT minigenes and reverse transcriptase PCR on mRNA isolated from leukocytes of the patient, this gene defect was shown to cause a null allele as the result of complete intron retention. In conclusion, we demonstrated that a point mutation in a lariat branchpoint consensus sequence causes a null allele in a patient with FED. In addition, our finding illustrates the importance of this sequence for normal human mRNA processing. Finally, this report provides a widely applicable strategy which ensures fast and effective screening for intronic defects that underlie differential gene expression.
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PMID:An intronic mutation in a lariat branchpoint sequence is a direct cause of an inherited human disorder (fish-eye disease). 875 45

Metabotropic glutamate receptor subtype 6 (mGluR6) is restrictedly expressed in the retinal ON bipolar cells and ablation of mouse mGluR6 by gene targeting results in a loss of ON responses to light stimulus and impairs the detection of visual contrasts. We have isolated genomic clones containing the human mGluR6 gene and determined the whole nucleotide sequence of the mGluR6 gene. The transcription initiation site of the human mGluR6 gene has been identified using primer extension analysis in combination with reverse transcriptase-mediated polymerase chain reaction analysis of human retinal RNA, while the termination of the mGluR6 mRNA has been assigned by the analysis of rapid amplification of 3'-cDNA ends. The human mGluR6 gene consists of 16,742 base pairs with 10 exons separated by nine introns. The human mGluR6 is composed of 877 amino acid residues with a signal peptide of 24 amino acid residues and the mature protein shows a 94.6% homology with the rat counterpart. A CpG-rich island is present at exon 1 and its preceding putative promoter region and this unusual sequence, like several tissue-specific genes, may be important for a specific expression of the mGluR6 gene in the retinal bipolar cells. The human mGluR6 gene has been mapped to chromosome 5q35 by the analyses of blot hybridization of a DNA panel of human/mouse/hamster somatic cell hybrids and fluorescence in situ hybridization of human chromosomes. This study should provide the genetic basis for not only better understanding the molecular mechanism underlying a tissue-specific expression of the mGluR6 gene but also exploring a potential defect in human mGluR6 in a certain inherited eye disease.
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PMID:The whole nucleotide sequence and chromosomal localization of the gene for human metabotropic glutamate receptor subtype 6. 921 6

We have previously identified a point mutation (intervening sequence (IVS) 4: T --> C) in the branchpoint consensus sequence of intron 4 of the lecithin:cholesterol acyltransferase (LCAT) gene in patients with fish-eye disease. To investigate the possible mechanisms responsible for the defective splicing, we made a series of mutations in the branchpoint sequence and expressed these mutants in HEK-293 cells followed by the analysis of pre-mRNA splicing using reverse transcriptase-polymerase chain reaction as well as LCAT activity assay. The results reveal that 1) the mutation of the branchpoint adenosine to any other nucleotide completely abolishes splicing; 2) the insertion of a normal branch site into the intronic sequence of the natural (IVS4-22c) or the branchpoint (IVS4-20t) mutant completely restores splicing; 3) the natural mutation can be partially rescued by making a single nucleotide change (G --> A) within the branchpoint consensus sequence; and 4) other single base changes, particularly around the branchpoint adenosine residue, significantly decrease the efficiency of splicing and thus enzyme activity. Surprisingly, the nucleotide transversion at the last position of the branchpoint sequence (i.e. IVS4-25a or -25g) results in a 2.7-fold increase in splicing efficiency. Therefore, these observations clearly establish the functional significance of the branchpoint sequence of intron 4 for the splicing of the human LCAT mRNA precursors.
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PMID:Characterization of the effects of mutations in the putative branchpoint sequence of intron 4 on the splicing within the human lecithin:cholesterol acyltransferase gene. 1084 35