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1.
M. Stodolsky 《Genetics》1974,78(3):809-822
An Hfr13 Delta(proA-lac) deletion recipient, -Delta(proA-lac)-F-purE(+)-, has been utilized in a study of the origins of duplications formed during chromosome fragment integration. Among the Pro(-)Lac(+) transductants, some have duplications spanning the F locus. These transductants are, or segregate, strains with F' episomes carrying genes of the duplication. Some of the duplications include purE(+), a gene which is not coinherited with lac(+) during bacteriophage P1-mediated transduction. Thus recipient genes have been duplicated during recombinant formation. Crossing-over models including replication steps provide a basis for explaining the duplication process. 相似文献
2.
Merodiploidy in ESCHERICHIA COLI-SALMONELLA TYPHIMURIUM Crosses: The Role of Unequal Recombination between Ribosomal RNA Genes 总被引:2,自引:0,他引:2
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Previous workers have shown that intergeneric crosses between Salmonella typhimurium and Escherichia coli produce a high proportion of merodiploid recombinants among the viable progeny. We have examined the unequal cross-over event that was responsible for a number of intergeneric merodiploids. The merodiploids that we studied were all heterozygous for the metB-argH interval and were the products of intergeneric conjugal crosses. We found that when the S. typhimurium donor had its transfer origin closely linked to metB and argH, all recombinants examined were merodiploid, and they generally arose as F-prime factors. Many of these F-prime factors had been created by recombination between flanking rrn genes in the donor. When the S. typhimurium Hfr transfer origin was more distant from the selected markers, quite different results were obtained. Depending on the donor, 19-47% of the recombinants that acquired the donor argH+ or metB+ genes were merodiploid for these loci, but none of the recombinants were F-prime. A majority of the merodiploids had a novel (nonparental) rrn gene, indicating that unequal recombination between nonidentical rrn genes was a prevalent mechanism for establishing the merodiploidy. Both tandem and nontandem duplications were found. Some of the merodiploids duplicated E. coli genes in addition to acquiring S. typhimurium genes. Some merodiploids contained the oriC region from each parent. Of a total of 118 intergeneric merodiploids characterized from all donors, 48 different genotypes were observed, and 38 of the 48 had one or more nonparental rrn operons. 相似文献
3.
Amber mutants of T1 were grown on each of three donor strains which were identical except that they carried different suppressors: respectively, supD, supE, and supB. The efficiency with which the mutants were able to transduce was tested after growth on each donor. In general, it was found that functions which control the synthesis of phage DNA usually caused significant increases in the efficiency of transduction (EOT). A few mutants located in genes essential for head production caused significant decreases in EOT. The presence of a particular suppressor in a donor can cause noteworthy changes in the EOT by certain of the mutant phages. Amber mutations in gene 3 of T1 were extremely sensitive to the particular suppressor present in the donor, showing a 17-fold decrease in EOT compared with other mutants after growth in donors with the supD suppressor and a 75-fold increase after growth in supE donors. Increases in EOT by early genes of T1 do not seem to be caused by a lack of competition of bacterial DNA with phage DNA during packaging since, in most instances, infective phage were produced in relatively normal amounts compared with wild-type T1. Phage DNA synthesis and degradations of the host chromosome are closely coupled in T1 infections; we believe that increases in EOT by mutants of early functions are due to inefficient degradation of the host chromosome. 相似文献
4.
Haptoglobin (Hp) is a hemoglobin-binding plasma protein consisting of two types of chains, called α and β, which originate
from a common polypeptide. In humans, but not in other mammals, Hp has been shown to occur in two allelic forms, Hp1 and Hp2,
which differ in the length of the α-chain. The longer α-chain (in Hp2) seems to have arisen by an internal duplication of
a gene segment coding for almost the entire α-chain of Hp1. In this article we show that Hp of cow (Bos taurus) contains an α-chain, the structure of which is similar to that of the human Hp2 α-chain. Furthermore, comparison of the
structure of bovine Hp and human Hp2 suggests that the bovine gene arose by a duplication of the gene segment homologous to that duplicated in human Hp2. However, a phylogenetic analysis indicates that the two genes were formed independently. The evolutionary pressure that
has led to the fixation of the Hps with a longer α-chain is not known.
Reviewing
Editor: Dr. Manyuan Long 相似文献
5.
Nicolas Puillandre Maren Watkins Baldomero M. Olivera 《Journal of molecular evolution》2010,70(2):190-202
A remarkable diversity of venom peptides is expressed in the genus Conus (known as “conotoxins” or “conopeptides”). Between 50 and 200 different venom peptides can be found in a single Conus species, each having its own complement of peptides. Conopeptides are encoded by a few gene superfamilies; here we analyze
the evolution of the A-superfamily in a fish-hunting species clade, Pionoconus. More than 90 conopeptide sequences from 11 different Conus species were used to build a phylogenetic tree. Comparison with a species tree based on standard genes reveals multiple gene
duplication events, some of which took place before the Pionoconus radiation. By analysing several A-conopeptides from other Conus species recorded in GenBank, we date the major duplication events after the divergence between fish-hunting and non-fish-hunting
species. Furthermore, likelihood approaches revealed strong positive selection; the magnitude depends on which A-conopeptide
lineage and amino-acid locus is analyzed. The four major A-conopeptide clades defined are consistent with the current division
of the superfamily into families and subfamilies based on the Cys pattern. The function of three of these clades (the κA-family,
the α4/7-subfamily, and α3/5-subfamily) has previously been characterized. The function of the remaining clade, corresponding
to the α4/4-subfamily, has not been elucidated. This subfamily is also found in several other fish-hunting species clades
within Conus. The analysis revealed a surprisingly diverse origin of α4/4 conopeptides from a single species, Conus bullatus. This phylogenetic approach that defines different genetic lineages of Conus venom peptides provides a guidepost for identifying conopeptides with potentially novel functions. 相似文献
6.
Yuichi Narita Sen-ichi Oda Osamu Takenaka Takashi Kageyama 《Journal of molecular evolution》2010,70(4):313-324
Fourteen different pepsinogen-A cDNAs and one pepsinogen-C cDNA have been cloned from gastric mucosa of the orangutan, Pongo pygmaeus. Encoded pepsinogens A were classified into two groups, i.e., types A1 and A2, which are different in acidic character. The
occurrence of 9 and 5 alleles of A1 and A2 genes (at least 5 and 3 loci), respectively was anticipated. Respective orthologous
genes are present in the chimpanzee genome although their copy numbers are much smaller than those of the orangutan genes.
Only A1 genes are present in the human probably due to the loss of the A2 gene. Molecular phylogenetic analyses showed that
A1 and A2 genes diverged before the speciation of great hominoids. Further reduplications of respective genes occurred several
times in the orangutan lineage, with much higher frequencies than those occurred in the chimpanzee and human lineages. The
rates of non-synonymous substitutions were higher than those of synonymous ones in the lineage of A2 genes, implying the contribution
of the positive selection on the encoded enzymes. Several sites of pepsin moieties were indeed found to be under positive
selection, and most of them locate on the surface of the molecule, being involved in the conformational flexibility. Deduced
from the known genomic structures of pepsinogen-A genes of primates and other mammals, the duplication/loss were frequent
during their evolution. The extreme multiplication in the orangutan might be advantageous for digestion of herbaceous foods
due to the increase in the level of enzymes in stomach and the diversification of enzyme specificity. 相似文献
7.
Ricardo M. Ferreira José Luiz Rybarczyk-Filho Rodrigo J. S. Dalmolin Mauro A. A. Castro José C. F. Moreira Leonardo G. Brunnet Rita M. C. de Almeida 《PloS one》2013,8(2)
Whole genome protein-protein association networks are not random and their topological properties stem from genome evolution mechanisms. In fact, more connected, but less clustered proteins are related to genes that, in general, present more paralogs as compared to other genes, indicating frequent previous gene duplication episodes. On the other hand, genes related to conserved biological functions present few or no paralogs and yield proteins that are highly connected and clustered. These general network characteristics must have an evolutionary explanation. Considering data from STRING database, we present here experimental evidence that, more than not being scale free, protein degree distributions of organisms present an increased probability for high degree nodes. Furthermore, based on this experimental evidence, we propose a simulation model for genome evolution, where genes in a network are either acquired de novo using a preferential attachment rule, or duplicated with a probability that linearly grows with gene degree and decreases with its clustering coefficient. For the first time a model yields results that simultaneously describe different topological distributions. Also, this model correctly predicts that, to produce protein-protein association networks with number of links and number of nodes in the observed range for Eukaryotes, it is necessary 90% of gene duplication and 10% of de novo gene acquisition. This scenario implies a universal mechanism for genome evolution. 相似文献
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Gene duplication is one of the major driving forces shaping genome and organism evolution and thought to be itself regulated by some intrinsic properties of the gene. Comparing the essential genes among mouse and human, we observed that the essential genes avoid duplication in mouse while prefer to remain duplicated in humans. In this study, we wanted to explore the reasons behind such differences in gene essentiality by cross-species comparison of human and mouse. Moreover, we examined essential genes that are duplicated in humans are functionally more redundant than that in mouse. The proportion of paralog pseudogenization of essential genes is higher in mouse than that of humans. These duplicates of essential genes are under stringent dosage regulation in human than in mouse. We also observed slower evolutionary rate in the paralogs of human essential genes than the mouse counterpart. Together, these results clearly indicate that human essential genes are retained as duplicates to serve as backed up copies that may shield themselves from harmful mutations. 相似文献
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TNF受体家庭介导的细胞凋亡信号转导 总被引:4,自引:1,他引:4
肿瘤坏死因子(TNF)家庭是一类多功能的细胞因子,具有诱导细胞凋亡、抗病毒、免疫调节等多种生物学活性,其中一些成员可以通过和细胞膜上相应受体结合,启动细胞内的凋亡机制,而诱导细胞凋亡,一些蛋白质(如TRADD、FADD、RIP、RAIDD等)参与这些信号传递过程,越来赵多的TNF家庭成员,TNF受体以及与细胞凋亡相产在的Caspase蛋白酶2成员被人们发现。 相似文献
13.
TNF受体家族介导的细胞凋亡信号转导 总被引:4,自引:0,他引:4
肿瘤坏死因子(TNF)家族是一类多功能的细胞因子,具有诱导细胞凋亡、抗病毒、免疫调节等多种生物学活性.其中一些成员可以通过和细胞膜上相应受体(即TNF受体家族成员)结合,启动细胞内的凋亡机制,而诱导细胞凋亡.一些蛋白质(如TRADD、FADD、RIP、RAIDD等)参与这些信号传递过程.越来越多的TNF家族成员、TNF受体以及与细胞凋亡相关的Caspase蛋白酶家族成员被人们发现. 相似文献
14.
Transduction of Methicillin Resistance in Staphylococcus aureus Dependent on an Unusual Specificity of the Recipient Strain 总被引:26,自引:11,他引:15
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Resistance to methicillin was transduced by phage 80 or 53 from two naturally occurring methicillin-resistant strains of Staphylococcus aureus to methicillin-susceptible recipient strains at frequencies of 10−7 to 10−9. Ultraviolet irradiation of transducing phage and posttransductional incubation at 30 C were essential for useful frequencies of transduction. Effectiveness as a recipient for this transduction was highly specific. Strain NCTC 8325 (PS47) in its native state was an ineffective recipient but became effective after it had received by transduction one of several penicillinase plasmids. This acquired effectiveness was retained in most cases after elimination of the plasmid by ethidium bromide treatment. Like the donor strain, the progeny were heterogeneous in the degree of their resistance to methicillin, which was expressed by a higher proportion of cells as the temperature of incubation was lowered from 37 to 30 C. Separate transductants varied widely in the degree of resistance acquired by transduction. Methicillin resistance was stable in the donor and transductant strains. We favored the interpretation that methicillin resistance in our strains was determined by a single chromosomal gene, although the possibility that it was determined by two or more closely linked genes could not be excluded. 相似文献
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H. T. Solheim C. Sekse A. M. Urdahl Y. Wasteson L. L. Nesse 《Applied and environmental microbiology》2013,79(3):896-900
Dissemination of Shiga toxin (Stx)-encoding bacteriophages is the most likely mechanism for the spread of Stx-encoding genes and the emergence of new Stx-producing Escherichia coli (STEC). Biofilm has been reported to be a place where horizontal gene transfer by plasmid conjugation and DNA transformation may occur, and in this study, horizontal gene transfer by transduction has been demonstrated. Transfer of Stx-encoding bacteriophages to potentially pathogenic E. coli in biofilm was observed at both 20°C and 37°C. The infection rates were higher at 37°C than at 20°C. To our knowledge, this study is the first to show lateral gene transfer in biofilm mediated by a temperate bacteriophage. The study shows that the biofilm environment can be suitable for transduction events and can thereby be an environment for the emergence of new pathogenic E. coli. 相似文献
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目的:建立具有组织特异性的鼻咽癌基因表达谱,筛选鼻咽癌中信号转导相关基因。方法:采用深圳微芯公司基于玻片的包含8046个人类基因的基因芯片,检测7例鼻咽癌组织及1例鼻咽炎组织,初步获得鼻咽癌异常表达基因;结合GO分类从异常表达的基因中筛选信号转导相关基因,以Biocarta信号通路数据库查询筛选基因相关转导信号通路信息。结果:在鼻咽癌组织独得1241个异常用表达基因,其中高表达基因871个,低表达基因343个。发现28个差异表达基因与细胞的信号转导相关,其中表达上调的21个,表达下调的7个。结论:成功建立了具有组织特异性的鼻咽癌基因表达谱,初步获得了鼻咽癌信号转导相关基因。 相似文献
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Sequence of Genes Replicated in Salmonella typhimurium as Examined by Transduction Techniques 总被引:7,自引:3,他引:4
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5-Bromouracil (BU) was pulsed into the genome of synchronously growing cells of an F(-) strain of Salmonella typhimurium of LT2. BU-labeled genes were transduced with P22 phage to a series of recipient auxotrophs. When BU was incorporated early in the replication cycle, the transducing markers that had hybrid densities were those that lie between 9 and 12 o'clock on the genetic map. When BU was incorporated during the terminal period of the synchronous cycle, the transducing particles had hybrid densities for genes that lie from 1 to 8 o'clock clockwise. When phages were prepared on cells in which the middle period was BU-labeled, transducing particles with hybrid densities appeared for genes that lie in two separate regions: between 7 and 9 o'clock and between 12 and 2 o'clock. Analysis of the map sequences of the transduced BU genes, the relative frequency of transduction for each marker, and the time sequence of replication led to a hypothesis that the origin of replication is near the isoleucine-valine gene on the chromosome map. As for direction of replication, several models were considered, including the possibility that replication may proceed in both directions in the same chromosome. It was also found that the aroB, cysG, and strA genes are cotransduced and strA and aroC are also cotransduced. The relative order of the four genes was found to be aroB, cysG, strA, aroC, but the orientation in the circular map was not determined. 相似文献