The structure and evolution of the two nonallelic rat preproinsulin genes.

In the rat, there are two nonallelic genes for preproinsulin. The insulin end products are very similar and are equally expressed. We have isolated clones carrying these genes and their flanking sequences, and characterized them by DNA sequencing and electron microscopic analysis. We have established the primary structure of the preproinsulin mRNAs and the signal peptides of these two proteins. One of the genes contains two introns: a 499 bp intron interrupting the region encoding the connecting peptide and a 119 bp intron interrupting the segment encoding the 5 noncoding region of the mRNA. The introns are transcribed and present in a preproinsulin mRNA precursor. The other gene possesses the smaller, but not the larger, of the two introns. Calculations based on the divergence of the two preproinsulin nucleotide and amino acid sequences indicate that these genes are the products of a recent duplication. Thus one of the genes gained or lost an intron since that time.     

东亚钳蝎蝎毒素BmKBT基因组序列的克隆及其分析

东亚钳蝎 (ButhusmartensiiKarsch ,BmK)蝎毒素BmKBT(又名BmKabT)是一个在初级结构上相似于β类哺乳动物毒素和功能接近于α类哺乳动物毒素的Na+ 通道毒素 .基于从毒腺cDNA文库中筛选得到的全长BmKBT前体核苷酸序列设计引物 ,以蝎基因组总DNA为模板进行聚合酶链式反应 (PCR) ,将PCR产物克隆至T载体、测序 .序列分析表明 :在BmKBT信号肽编码区的 3′端的- 4位Gly密码子的第 1位与第 2位碱基中有 1个长 2 2 5nt的内含子 ,插入位点距离该基因的起始密码子 4 6nt ,AT含量为 78 7% ,其内含子可能的剪接分枝位点距离 3′剪接受体位点 4 7nt.内含子的大小及其基因组织结构分析表明 :BmKBT具有与α类哺乳动物毒素类似的基因组织结构 ,进一步说明BmKBT是一个介于α类和β类Na+ 通道毒素之间的中间型蝎毒素 ,可以作为研究蝎毒素分子进化的合适材料     

Intron requirement for expression of the human purine nucleoside phosphorylase gene.

Abbreviated purine nucleoside phosphorylase (PNP) genes were engineered to determine the effect of introns on human PNP gene expression. PNP minigenes containing the first intron (complete or shortened from 2.9 kb down to 855 bp), the first two introns or all five PNP introns resulted in substantial human PNP isozyme expression after transient transfection of murine NIH 3T3 cells. Low level human PNP activity was observed after transfection with a PNP minigene containing the last three introns. An intronless PNP minigene construct containing the PNP cDNA fused to genomic flanking sequences resulted in undetectable human PNP activity. Heterogeneous, stable NIH 3T3 transfectants of intron-containing PNP minigenes (verified by Southern analysis), expressed high levels of PNP activity and contained appropriately processed 1.7 kb message visualized by northern analysis. Stable transfectants of the intronless PNP minigene (40-45 copies per haploid genome) contained no detectable human PNP isozyme or mRNA. Insertion of the 855 bp shortened intron 1 sequence in either orientation upstream or downstream of a chimeric PNP promoter-bacterial chloramphenicol acetyltransferase (CAT) gene resulted in a several-fold increase in CAT expression in comparison with the parental PNP-CAT construct. We conclude that human PNP gene expression at the mRNA and protein level is dependent on the presence of intronic sequences and that the level of PNP expression varies directly with the number of introns included. The disproportionately greatest effect of intron 1 can be explained by the presence of an enhancer-like element retained in the shortened 855 bp intron 1 sequence.     

一个东亚钳蝎蝎毒素BmTXKβ基因的克隆及其基因表达调控

从东亚钳蝎 (ButhusmartensiiKarsch ,BmK)毒腺组织cDNA文库中分离的长链钾通道毒素BmTXKβcDNA序列 ,克隆了BmTXKβ基因组序列 .BmTXKβ基因含有一个长度为 886bp的内含子 ,定位于BmTXKβ成熟肽中 ,与其它蝎毒素基因内含子定位于信号肽的基因结构不同 .并且 ,BmTXKβ基因的内含子特征也与其它蝎毒素基因不同 .研究结果从基因水平上证实了BmTXKβ是一个新的蝎毒素样肽 .以BmTXKβcDNA序列为探针与蝎基因组DNASouthern杂交出现 2条特异性杂交带 .杂交结果为蝎毒素基因可能通过DNA重排、多拷贝或多基因家族来调控基因表达提供了证据 .     

Distinct roles of the first introns on the expression of Arabidopsis profilin gene family members

Profilin is a small actin-binding protein that regulates cellular dynamics of the actin cytoskeleton. In Arabidopsis (Arabidopsis thaliana), five profilins were identified. The vegetative class profilins, PRF1, PRF2, and PRF3, are expressed in vegetative organs. The reproductive class profilins, PRF4 and PRF5, are mainly expressed in pollen. In this study, we examined the role of the first intron in the expression of the Arabidopsis profilin gene family using transgenic plants and a transient expression system. In transgenic plants, we examined PRF2 and PRF5, which represent vegetative and reproductive profilins. The expression of the PRF2 promoter fused with the beta-glucuronidase (GUS) gene was observed in the vascular bundles, but transgenic plants carrying the PRF2 promoter-GUS with its first intron showed constitutive expression throughout the vegetative tissues. However, the first intron of PRF5 had little effect on the reporter gene expression pattern. Transgenic plants containing PRF5 promoter-GUS fusion with or without its first intron showed reproductive tissue-specific expression. To further investigate the different roles of the first two introns on gene expression, the first introns were exchanged between PRF2 and PRF5. The first intron of PRF5 had no apparent effect on the expression pattern of the PRF2 promoter. But, unlike the intron of PRF5, the first intron of PRF2 greatly affected the reproductive tissue-specific expression of the PRF5 promoter, confirming a different role for these introns. The results of a transient expression assay indicated that the first intron of PRF1 and PRF2 enhances gene expression, whereas PRF4 and PRF5 do not. These results suggest that the first introns of profilin genes are functionally distinctive and the first introns are required for the strong and constitutive gene expression of PRF1 and PRF2 in vegetative tissues.     

The legumin gene family: structure of a B type gene of Vicia faba and a possible legumin gene specific regulatory element.

The field bean, Vicia faba L. var. minor, possesses two sub-families of 11 S legumin genes named A and B. We isolated from a genomic library a B-type gene (LeB4) and determined its primary DNA sequence. Gene LeB4 codes for a 484 amino acid residue prepropolypeptide, encompassing a signal peptide of 22 amino acid residues, an acidic, very hydrophilic alpha-chain of 281 residues and a basic, somewhat hydrophobic beta-chain of 181 residues. The latter two coding regions are immediately contiguous, but each is interrupted by a short intron. Type A legumin genes from soybean and pea are known to have introns in the same two positions, in addition to an extra intron (within the alpha-coding sequence). Sequence comparisons of legumin genes from these three plants revealed a highly conserved sequence element of at least 28 bp, centered at approximately 100 bp upstream of each cap site. The element is absent from the equivalent position of all non-legumin and other plant and fungal genes examined. We tentatively name this element "legumin box" and suggest that it may have a function in the regulation of legumin gene expression.     

Intron-size constraint as a mutational mechanism in Rothmund-Thomson syndrome

Rothmund-Thomson syndrome (RTS) is an autosomal recessive disorder caused by deleterious mutations in the RECQL4 gene on chromosome 8. The RECQL4 gene structure is unusual because it contains many small introns <100 bp. We describe a proband with RTS who has a novel 11-bp intronic deletion, and we show that this mutation results in a 66-bp intron too small for proper splicing. Constraint on intron size may represent a general mutational mechanism, since human-genome analysis reveals that approximately 15% of genes have introns <100 bp and are therefore susceptible to size constraint. Thus, monitoring of intron size may allow detection of mutations missed by exon-by-exon approaches.     

Evolution of RH genes in hominoids: characterization of a gorilla RHCE-like gene

The human RH locus is responsible for the expression of the Rh blood group antigens. It consists of two closely linked genes, RHD and RHCE, that exhibit 92% similarity between coding regions. These observations suggest that they are derived from a relatively recent duplication event. Previously a study of nonhuman primate RH-like genes demonstrated that ancestral RH gene duplication occurred in the common ancestor of man, chimpanzees and gorillas. By amplification of intron 3 and intron 4 of gorilla RH-like genes, we have now shown that, like man, gorillas possess two types of RH intron 3 (RHCE intron 3 being 289 bp longer than the RHD intron 3) and two types of intron 4 (RHCE intron 4 being 654 bp longer than the RHD intron 4). Here we report the characterization of a cDNA encoded by a gorilla RH-like gene which possesses introns 3 and 4 of the RHCE type. A comparison of this gorilla RHCE-like coding sequence with previously characterized human and ape cDNA sequences suggests that RH genes experienced complex recombination events after duplication in the common ancestor of humans, chimpanzees and gorillas.     

Pheromone 4 gene of Euplotes octocarinatus.

We have cloned and sequenced a 1.7 kb macronuclear chromosome encoding the pheromone 4 gene of Euplotes octocarinatus. The sequence of the secreted pheromone is preceded by a 42 amino acid leader peptide, which ends with a lysine residue. The sequence coding for the leader peptide contains information for a putative signal peptide and is interrupted by a 772 bp intron as shown by comparison with a cDNA clone. A 64 bp intron and a 145 bp intron interrupt the sequence coding for the secreted pheromone. The three introns contain typical 5' and 3' splice junctions and a putative branch point site. The small introns have a low GC content. The large intron has a GC content similar to that of the pheromone 4 gene exons. The amino acid sequence of pheromone 4, deduced from both the genomic DNA and the cDNA of pheromone 4, shows that the secreted pheromone consists of 85 amino acids. One of its amino acids is encoded by a UGA codon. Since it has been shown for pheromone 3 of E. octocarinatus that UGA is translated as cysteine, it is assumed that the UGA codon encodes cysteine in pheromone 4 as well. The 164 bp noncoding region upstream of the leader peptide is AT-rich and contains an inverted repeat capable of forming a stem-loop structure with a stem of 11 bp. The 151 bp noncoding region at the 3' end of the chromosome contains a putative polyadenylation sequence and an inverted repeat. The macronuclear molecule is flanked by telomeres and carries the pentanucleotide motif TTGAA, located at a distance of 17 nucleotides from the telomeres. This motif has been suggested to be involved in the formation of macronuclear chromosomes.     

Nucleotide sequence and intron structure of the apocytochrome b gene of Neurospora crassa mitochondria

The sequence of the apocytochrome b (cob) gene of Neurospora crassa has been determined. The structural gene is interrupted by two intervening sequences of approximately 1260 bp each. The polypeptide encoded by the exons shows extensive homology with the cob proteins of Aspergillus nidulans and Saccharomyces cerevisiae (79% and 60%, respectively). The two introns are, however, located at sites different from those of introns in the cob genes of A. nidulans and S. cerevisiae (which contain highly homologous introns at the same site within the gene). The introns share several short regions of sequence homology (10-12 bp long) with each other and with other fungal mitochondrial introns. Moreover, the second intron contains a 50 nucleotide long sequence that is highly homologous with sequences within every ribosomal intron of fungal mitochondria sequenced to date. The conserved sequences may allow the formation of a core secondary structure, which is nearly identical in many mitochondrial introns. The conserved secondary structure may be required for intron splicing. The second intron contains an open reading frame, continuous with the preceding exon, of approximately 290 codons. Two stretches of 10 amino acid residues, conserved in many introns, are present in the open reading frame.     

Structure of the gene encoding potato cytosolic pyruvate kinase.

The polymerase chain reaction (PCR) has been used to generate a series of overlapping genomic clones representing 43 bp of 5' untranslated sequence, 63 bp of 3' untranslated sequence and the entire coding sequence of the gene encoding potato cytosolic pyruvate kinase (PKc). This portion of the gene is approximately 4.5 kb in length and is interrupted by three introns, one of which is present in the 5' untranslated region. Southern blot analysis indicates that PKc is encoded by a small gene family, and sequence data from a number of PCR-derived genomic clones indicate that there are as many as six PKc genes. Sequence differences between the PCR-generated genomic clones and a PKc cDNA clone are discussed with respect to the fidelity of Taq polymerase. An alignment of intron placement in the potato PKc gene with intron placement in PK genes from other sources indicates that two of the potato introns correspond to intron positions in other species.     

鲤鱼sGnRH基因克隆及其在成熟个体的表达分析

采用RACE方法,从鲤鱼脑组织克隆了两个差异的sGnRH(salmon GnRH[Trp^7Leu^8]GnRH)cDNAs,即cDNA1和cDNA2,其长度分别为393和478bp。两个cDNAs都包括一个285bp开放阅读框,编码的sGnRH前体为94个氨基酸残基,由一个信号肽、sGnRH十肽和一个由蛋白水解位点(Gly-Lys-Arg)连接的促性腺激素释放激素相关肽共3部分组成。用内含子捕获得到相应的两个差异sGnRH基因,即sGnRH genel和gene2,其基本结构都包括4个外显子和3个内含子,3个内含子的核苷酸相似性分别为71．1％、76．1％和88．0％。鲤鱼sGnRH cDNAs及基因的基本结构和编码特点与已报道的不同形式GnRH cDNAs和GnRH基因相似,由此推测所有类型的GnRH可能来自一个共同的祖分子。Southern杂交进一步证实鲤鱼基因组存在两个不同的sGnRH基因座位。相对定量RT-PCR检测发现,两个sGnRH基因除在精巢的表达存在差异外,在脑区、垂体和成熟卵巢共表达。其中两个sGnRH基因在端脑和下丘脑的表达水平明显高于后脑区。根据sGnRH mRNAs在多个脑区、性腺和垂体的共存推测,sGnRH可能对鲤鱼下丘脑-垂体-性腺轴的调节有至关重要作用,同时可能起神经调节剂或自分泌和旁分泌调节因子的作用。     

The exon/intron organization of the globin gene of Scapharca inaequivalvis homodimeric hemoglobin: unusual intron homology with other bivalve mollusc globin genes

In this study, we have investigated the positions of introns in the globin gene of Scapharca inaequivalvis homodimeric hemoglobin. We found the three exon/two intron organization typical of vertebrate globin genes, with the two introns in highly conserved positions, as it occurs in the A and B globin genes of the tetrameric hemoglobin from the same organism, confirming the absence of the so-called `central intron' found in the globin genes of plants and of some invertebrates. We identified two homodimeric globin genes (3207 and 2723 bp) that differ only with respect to the size of the first intron. Sequence analysis of the two first introns (1668 and 1364 bp) has revealed that they are highly homologous, except for a 569- and 296-bp insertion in each intron I. Interestingly, the two first introns contain regions with an unusually high identity (∼80%) with regions of the first intron of the congeneric clam Anadara trapezia and the related clam Barbatia reveana globin genes, suggesting that these uncoding regions may have played a regulatory role that has subsequently been lost during the course of the evolution.     

The effects of a stimulating intron on the expression of heterologous genes in Arabidopsis thaliana

Introns are often added to transgenes to increase expression, although the mechanism through which introns stimulate gene expression in plants and other eukaryotes remains mysterious. While introns vary in their effect on expression, it is unknown whether different genes respond similarly to the same stimulatory intron. Furthermore, the degree to which gene regulation is preserved when expression is increased by an intron has not been thoroughly investigated. To test the effects of the same intron on the expression of a range of genes, GUS translational fusions were constructed using the promoters of eight Arabidopsis genes whose expression was reported to be constitutive (GAE1, CNGC2 and ROP10), tissue specific (ADL1A, YAB3 and AtAMT2) or regulated by light (ULI3 and MSBP1). For each gene, a fusion containing the first intron from the UBQ10 gene was compared to fusions containing the gene's endogenous first intron (if the gene has one) or no intron. In every case, the UBQ10 intron increased expression relative to the intronless control, although the magnitude of the change and the level of expression varied. The UBQ10 intron also changed the expression patterns of the CNGC2 and YAB3 fusions to include strong activity in roots, indicating that tissue specificity was disrupted by this intron. In contrast, the regulation of the ULI3 and MSBP1 genes by light was preserved when their expression was stimulated by the intron. These findings have important implications for biotechnology applications in which a high level of transgene expression in only certain tissues is desired.     

东亚钳蝎毒素BmKT四个同源基因的克隆及基因组织分析

BmKT是从本室构建的cDNA文库中筛选到的1个α钠通道毒素,根据其全长cDNA序列设计引物,采用PCR法以蝎总基因组DNA为模板,获得4个BmKT的同源基因,分别命名为BmKT′和BmKTa、BmKTb、BmKTb′.序列分析表明：BmKT′和BmKTa基因含有大小分别为509 bp和506 bp的内含子,位于信号肽编码区内,插入信号肽-4位残基Gly密码子的第一个碱基G之后;而BmKTb和BmKTb′ 的内含子大小均为418 bp．这4个BmKT的同源基因内含子符合GT/AG拼接规律,其中BmKT′和BmKTa的内含子A+T含量分别为61.7%和61.9%,低于目前已报导的大多数蝎毒素基因A+T含量,大大低于它们第一外显子A+T含量（71.7%）,略高于第二外显子A+T含量（55.5%）;而BmKTb,BmKTb′的内含子A+T含量分别为75.8%和76.1%,与目前已报导的大多数蝎毒素基因A+T含量相似．BmKT′基因的外显子与BmKT基因cDNA所对应氨基酸序列仅在信号肽中-7位有一个氨基残基的差异（BmKT: Leu→BmKTa: Val）;而BmKTa基因外显子所推断的氨基酸序列与BmKT前体比较,则在成熟肽的+54位发生了突变（BmKT: Lys→BmKTa: Asn）,是与BmKT同源的一个新基因．BmKTb基因和BmKTb′基因所编码的前体肽与BmKT基因对应的前体肽同源性约为65%,显然BmKTb和BmKTb′是不同于BmKT的2个新基因（GenBank登录号: BmKT′, AY786186; BmKTa, AY676142; BmKTb, AY676140; BmKTb′, AY676141）