Regulation of the β-hydroxyacyl ACP dehydratase gene of <Emphasis Type="Italic">Picea mariana</Emphasis> by alternative splicing

The gene for β-hydroxyacyl ACP dehydratase, a de novo fatty acid biosynthetic enzyme, was cloned from Picea mariana (black spruce) and consists of five exons and four introns. The first intron of the β-hydroxyacyl ACP dehydratase mRNA is alternatively spliced. Retention of intron 1 in splice variants results in truncation of the β-hydroxyacyl ACP dehydratase ORF at a premature termination codon. In addition, splicing of intron 1 was found to be associated with cold temperature. mRNAs retaining intron 1 increase with seed imbibition at 22°C but not 4°C, whereas, splicing of intron 1 increases in winter weeks with temperatures below freezing. These results provide evidence that alternative splicing may also contribute to regulation of lipid biosynthesis in Picea mariana.     

Protein encoded by the third intron of cytochrome b gene in Saccharomyces cerevisiae is an mRNA maturase. Analysis of mitochondrial mutants, RNA transcripts proteins and evolutionary relationships

We have established the nucleotide sequence of the wild-type and that of a trans-acting mutant located in the third (bi3) intron of the Saccharomyces cerevisiae mitochondrial cytochrome b gene. The intron, 1691 base-pairs long, has an open reading frame 1045 base-pairs long, in phase with the preceding exon and the mutation replaces the evolutionarily conserved Gly codon of the second consensus motif by an Asp codon and blocks the formation of mature cytochrome b mRNA. Splicing intermediates of 5300 and 3900 bases with unexcised bi3 intron and a characteristic novel polypeptide (p50), the size of which corresponds to the chimeric protein encoded by upstream exons and the bi3 intronic open reading frame (ORF), accumulate in this and other bi3 splicing-deficient mutants. We conclude that the protein encoded by the bi3 ORF is a specific mRNA maturase involved in the splicing of the cytochrome b mRNA. The open reading frame of the third intron is remarkably similar to that of the unique intron of the cytochrome b gene (cob A) of Aspergillus nidulans. Both are located in exactly the same position and possibly derive from a recent common ancestor by a horizontal transfer. We have established the nucleotide sequence of an exonic mutant located in the B3 exon. This missense mutation changes the Phe codon 151 into a Cys codon and leads to the absence of functional cytochrome b but does not affect splicing. Finally, we have studied the splicing pathway leading to the synthesis of cytochrome b mRNA by analysing, in a comprehensive manner, the 22 splicing intermediates of several mutants located in bi3.     

Analysis of mono-ADP-ribosyltransferase 4 gene expression in human monocytes: splicing pattern and potential regulatory elements

Mono-ADP-ribosyltransferase (ART) 4 belongs to a family of ectoenzymes that catalyze the transfer of ADP-ribose from NAD+ to a target protein. ART4 could be detected on HEL cells and erythrocytes by FACS analysis while it was absent from activated monocytes, despite the presence of ART4 mRNA in these cells. The predicted glycosylphosphatidylinositol (GPI) linkage of ART4 could be verified by showing that treatment of erythrocytes, HEL cells and ART4-transfected HEK-293-T cells with phosphatidylinositol-specific phospholipase C results in a decrease in ART4 expression. Furthermore, an ART4 construct carrying an Ala285Val mutation that is critical for the formation of a GPI anchor failed to be expressed in transfected C-33A cells. Analysis of the gene structure revealed that the first of the three exons was at least 236 bp longer than previously published and that splicing occurred in the coding region of the mRNA from HEL cells and monocytes. When carrying out 5' inverse RACE-PCR we confirmed the existence of 5 ATGs in the 5' untranslated region (5'UTR). By deletion and site-directed mutagenesis of the ATGs, we showed that the first two ATGs impair translation and that both the 3rd and 5th ATG can be used for translation initiation after expression in C-33A cells. On analysis of the 3'UTR, which contains 2 adenylate/uridylate-rich elements (AREs), we detected one variant in monocytes that would be devoid of a GPI-anchor signal and thus could represent a secreted form of ART4. Thus, alternative splicing and the use of regulatory elements in the 5'UTR and 3'UTR represent means to control ART4 expression.     

Dystrophin基因3-7号外显子缺失后下游新翻译区启动与BMD关系的生物信息学分析

目的:研究dystrophin基因3-7号外显子缺失后下游新翻译区启动与贝克氏肌营养不良(Becker muscular dystrophy,BMD)的关系及可能机制.方法:用生物信息学方法对dystrophin基因3-7号外显子缺失后可能的启动子、开放阅读框、翻译起始位点、蛋白疏水性性质改变及重要结构域进行分析.结果:3-7号外显子缺失后,起始于正常肌肉启动子的转录体,其翻译阅读框提前终止,但在8号外显子内可能启动一个新的翻译阅读框;内含子2或7里可能含有类似启动子的元件,也可能导致8号外显子内翻译区的启动.新阅读框编码的蛋白仍然保留有重要的功能区,患者可以表现为BMD.结论:dystrophin基因3-7号外显子缺失后下游新翻译区仍有存在启动的可能,患者可以表现为BMD表型.