Exon

About: Exon is a research topic. Over the lifetime, 38308 publications have been published within this topic receiving 1745408 citations. The topic is also known as: exons.

Sequence of the intron/exon junctions of the coding region of the human androgen receptor gene and identification of a point mutation in a family with complete androgen insensitivity.

Abstract: Androgens act through a receptor protein (AR) to mediate sex differentiation and development of the male phenotype. We have isolated the eight exons in the amino acid coding region of the AR gene from a human X chromosome library. Nucleotide sequences of the AR gene intron/exon boundaries were determined for use in designing synthetic oligonucleotide primers to bracket coding exons for amplification by the polymerase chain reaction. Genomic DNA was amplified from 46,XY phenotypic female siblings with complete androgen insensitivity syndrome. AR binding affinity for dihydrotestosterone in the affected siblings was lower than in normal males, but the binding capacity was normal. Sequence analysis of amplified exons demonstrated within the AR steroid-binding domain (exon G) a single guanine to adenine mutation, resulting in replacement of valine with methionine at amino acid residue 866. As expected, the carrier mother had both normal and mutant AR genes. Thus, a single point mutation in the steroid-binding domain of the AR gene correlated with the expression of an AR protein ineffective in stimulating male sexual development.

Rates of in situ transcription and splicing in large human genes.

Abstract: Transcription and splicing must proceed over genomic distances of hundreds of kilobases in many human genes. However, the rates and mechanisms of these processes are poorly understood. We have used the compound 5,6-dichlorobenzimidazole 1-beta-D-ribofuranoside (DRB), which reversibly blocks gene transcription in vivo, combined with quantitative RT-PCR to analyze the transcription and RNA processing of several long human genes. We found that the rate of RNA polymerase II transcription over long genomic distances is about 3.8 kb min(-1) and is similar whether transcribing long introns or exon-rich regions. We also determined that co-transcriptional pre-mRNA splicing of U2-dependent introns occurs within 5-10 min of synthesis, irrespective of intron length between 1 kb and 240 kb. Similarly, U12-dependent introns were co-transcriptionally spliced within 10 min of synthesis, confirming that these introns are spliced within the nuclear compartment. These results show that the expression of large genes is unexpectedly rapid and efficient.

Activation of the β-Catenin Gene in Primary Hepatocellular Carcinomas by Somatic Alterations Involving Exon 3

Abstract: We screened 75 primary hepatocellular carcinomas for somatic mutations in the entire coding region of the beta-catenin gene. We detected somatic mutations in 14 tumors; 12 were considered to cause amino acid substitutions and 2 were interstitial deletions of 51 or 195 nucleotides of genomic DNA, corresponding to exon 3. Among the 12 point mutations, 6 occurred at potential serine/threonine phosphorylation residues of codons 33, 41, or 45. The remaining six tumors contained a mutation at codon 32 (aspartic acid) or 34 (glycine), flanking to the serine residue at codon 33. By Western blot analysis, we confirmed accumulation of beta-catenin in five tumors for which frozen tissues were available; the five included tumors in which amino acid alterations had occurred at codons 32, 34, or 45, and one with a 17-amino acid deletion. Our results suggested that accumulation of beta-catenin due to amino acid substitutions at potential serine/threonine phosphorylation residues or at their neighboring codons or interstitial deletions involving exon 3 could contribute to hepatocellular carcinogenesis.

Signal-dependent regulation of splicing via phosphorylation of Sam68

Abstract: Evolution of human organismal complexity from a relatively small number of genes1,2—only approximately twice that of worm or fly—is explained mainly by mechanisms generating multiple proteins from a single gene, the most prevalent of which is alternative pre-messenger-RNA splicing1,3,4. Appropriate spatial and temporal generation of splice variants demands that alternative splicing be subject to extensive regulation, similar to transcriptional control. Activation by extracellular cues of several cellular signalling pathways can indeed regulate alternative splicing5,6,7,8. Here we address the link between signal transduction and splice regulation. We show that the nuclear RNA-binding protein Sam68 is a new extracellular signal-regulated kinase (ERK) target. It binds exonic splice-regulatory elements of an alternatively spliced exon that is physiologically regulated by the Ras signalling pathway, namely exon v5 of CD44. Forced expression of Sam68 enhanced ERK-mediated inclusion of the v5-exon sequence in mRNA. This enhancement was impaired by mutation of ERK-phosphorylation sites in Sam68, whereas ERK phosphorylation of Sam68 stimulated splicing of the v5 exon in vitro. Finally, Ras-pathway-induced alternative splicing of the endogenous CD44-v5 exon was abolished by suppression of Sam68 expression. Our data define Sam68 as a prototype regulator of alternative splicing whose function depends on protein modification in response to extracellular cues.