Duplicated Elements Research Articles

추상구문트리를 이용한 어스팩트 마이닝 프로세스 설계

어스팩트 지향 프로그래밍은 시스템에서 크로스커팅 개념을 추출하고 소프트웨어 모듈화를 통하여 기능의 분산과 코드의 혼란을 해결하기 위한 패러다임이다. 현존하는 어스팩트 개발 방법은 크로스커팅 대상 영역을 추출에 어려움이 있기 때문에, 어스팩트 마이닝을 적용하기가 쉽지 않다. 어스팩트 마이닝에서는 기존 프로그램의 리팩토링 요소를 크로스커팅 영역으로 변환하는 기술이 필수적이다. 본 논문에서는 리팩토링에 적합한 크로스커팅 영역 자동 추출을 위한 시스템에서 크로스커팅 개념을 추출하기 위한 어스팩트 마이닝 방법을 제안한다. 소스 모듈의 추상 구문구조 명세를 이용하여, 모듈의 구조적 중복 관계 요소를 추출한다. Apriori 알고리즘을 통하여 중복 구문트리를 생성하고, 크로스커팅 영역 대상인 중복된 소스 모듈을 자동 생성, 최적화 할 수 있다. Berkeley Yacc의 berbose.c 모듈을 제안하는 마이닝 프로세스에 적용해 본 결과, 원본 대비 9.47%의 길이와 부피의 감소하였고, CCFinder 대비 4.92%의 길이 감소, 5.11%의 부피 감소 효과를 확인하였다. Aspect-oriented programming is the paradigm which extracts crosscutting concern from a system and solves scattering of a function and confusion of a code through software modularization. Existing aspect developing method has a difficult to extract a target area, so it is not easy to apply aspect mining. In an aspect minning, it is necessary a technique that convert existing program refactoring elements to crosscutting area. In the paper, it is suggested an aspect mining technique for extracting crosscutting concern in a system. Using abstract syntax structure specification, extract functional duplicated relation elements. Through Apriori algorithm, it is possible to create a duplicated syntax tree and automatic creation and optimization of a duplicated source module, target of crosscutting area. As a result of applying module of Berkeley Yacc(berbose.c) to mining process, it is confirmed that the length and volume of program has been decreased of 9.47% compared with original module, and it has been decreased of 4.92% in length and 5.11% in volume compared with CCFinder.

Regulatory divergence of the duplicated chromosomal loci sox11a/b by subpartitioning and sequence evolution of enhancers in zebrafish

We used the classic example of the duplicated zebrafish sox11a and -b loci to test the duplication, degeneration, complementation (DDC) model of genome evolution through whole genome duplication. While recent reports have demonstrated sub-partitioning of regulatory sequences in duplicated regions, a comparison of the regulatory capabilities of extant regulatory sequences derived from ancient ancestral elements has been scarce. Consistent with the DDC model, we find that ancestral regulatory elements distributed over several hundred kb were lost in either one or the other zebrafish duplicate, leading to subpartitioning. However, regulatory sequences kept as duplicates near both sox11 co-orthologs diverged in sequence from each other and from human elements and in the regulatory patterns they drive in transgenic zebrafish. Evolutionary analysis of the loci suggested that both zebrafish protein coding sox11 orthologs have been maintained by purifying selection, and have evolved at comparable rates, indicative of non-diverged protein functions. The duplicated regulatory elements, conversely, evolved with different divergence rates and degrees of subfunctionalization. These data show that regulatory evolution of gene expression patterns occurred both through differential loss as well as through regulatory sequence evolution in zebrafish versus human genomes.

Implications of duplicated cis-regulatory elements in the evolution of metazoans: the DDI model or how simplicity begets novelty

The discovery that most regulatory genes were conserved among animals from distant phyla challenged the ideas that gene duplication and divergence of homologous coding sequences were the basis for major morphological changes in metazoan evolution. In recent years, however, the interest for the roles, conservation and changes of non-coding sequences grew-up in parallel with genome sequencing projects. Presently, many independent studies are highlighting the importance that subtle changes in cis-regulatory regions had in the evolution of morphology trough the Animal Kingdom. Here we will show and discuss some of these studies, and underscore the future of cis-Evo-Devo research. Nevertheless, we would also explore how gene duplication, which includes duplication of regulatory regions, may have been critical for spatial or temporal co-option of new regulatory networks, causing the deployment of new transcriptome scenarios, and how these induced morphological changes were critical for the evolution of new forms. Forty years after Susumu Ohno famous sentence 'natural selection merely modifies, while redundancy creates', we suggest the alternative: 'natural selection modifies, while redundancy of cis-regulatory elements innovates', and propose the Duplication-Degeneration-Innovation model to explain the increased evolvability of duplicated cis-regulatory regions. Paradoxically, making regulation simpler by subfunctionalization paved the path for future complexity or, in other words, 'to make it simple to make it complex'.

Extensive genomic copy number variation in embryonic stem cells

Recent analysis of the human and mouse genomes has revealed that highly identical duplicated elements account for >5% of the sequence content. These elements vary in copy number between individuals. Copy number variations (CNVs) contribute significantly to genetic differences among individuals and are increasingly recognized as a causal factor in human diseases with different etiologies. In inbred mouse strains, CNVs have been fixed by inbreeding, but they are highly variable among strains. Within strains, de novo germ-line CNVs can occur, leading to interindividual variation. By analyzing the genome of clonal isolates of mouse ES cells derived from common parental lines, we have uncovered extensive and recurrent CNVs. This variation arises during mitosis and can be cotransmitted into the mouse germ line along with engineered alleles, contributing to genetic variability. The frequency and extent of these genomic changes in ES cells suggests that all somatic tissues in individuals will be mosaics composed of variants of the zygotic genome. Human ES (hES) cells and derived somatic lineages may be similarly affected, challenging the concept of a stable somatic genome.

Ancient duplicated conserved noncoding elements in vertebrates: A genomic and functional analysis

Fish-mammal genomic comparisons have proved powerful in identifying conserved noncoding elements likely to be cis-regulatory in nature, and the majority of those tested in vivo have been shown to act as tissue-specific enhancers associated with genes involved in transcriptional regulation of development. Although most of these elements share little sequence identity to each other, a small number are remarkably similar and appear to be the product of duplication events. Here, we searched for duplicated conserved noncoding elements in the human genome, using comparisons with Fugu to select putative cis-regulatory sequences. We identified 124 families of duplicated elements, each containing between two and five members, that are highly conserved within and between vertebrate genomes. In 74% of cases, we were able to assign a specific set of paralogous genes with annotation relating to transcriptional regulation and/or development to each family, thus removing much of the ambiguity in identifying associated genes. We find that duplicate elements have the potential to up-regulate reporter gene expression in a tissue-specific manner and that expression domains often overlap, but are not necessarily identical, between family members. Over two thirds of the families are conserved in duplicate in fish and appear to predate the large-scale duplication events thought to have occurred at the origin of vertebrates. We propose a model whereby gene duplication and the evolution of cis-regulatory elements can be considered in the context of increased morphological diversity and the emergence of the modern vertebrate body plan.

Clustering, duplication and chromosomal distribution of mouse SINE retrotransposons

We analyzed potential mechanisms determining chromosomal distributions of the mouse B1 and B2 non-LTR retrotransposons, also known as SINE elements. We report that young B1 and B2 SINEs are underrepresented on chromosome X relative to autosomes, which is consistent with their integration in male germ lines. As the age of the SINE elements progresses, their densities on chromosome X increase relative to autosomal densities, possibly due to differences in ectopic recombination rates between chromosome X and autosomes. Furthermore, unlike young human Alus that tend to be integrated outside Alu-dense regions, young B1 and B2 elements are found mostly in SINE-rich clusters. The B1- or B2-rich clusters are more likely to contain duplicated elements than B1- or B2-poor chromosomal regions. We also present evidence indicating potential association of B1 and B2 elements with intra-chromosomal segmental duplications. No such association was found with inter-chromosomal duplications. We propose that the accumulation of mouse SINE elements observed in GC-rich regions may be due to the excess of DNA duplications over deletions in gene-rich regions that tend to be GC rich.

Long Inversely Oriented Subunits Form a Complex Monomer of Tribolium brevicornis Satellite DNA

Highly abundant satellite DNA named TBREV is detected and characterized in the beetle Tribolium brevicornis (Insecta: Coleoptera). An outstanding peculiarity of the TBREV satellite monomer is its complex structure based on the two approximately 470-bp-long subunits, inversely oriented within a 1061-bp-long monomer sequence. The proposed evolutionary history demonstrates a clear trend toward increased complexity and length of the TBREV satellite monomer. This tendency has been observed on three levels: first as direct and inverted duplications of short sequence motifs, then by inverse duplication of the approximately 470-bp sequence segment, and, finally, by spread of inversely duplicated elements in a higher-order register and formation of extant monomers. Inversely oriented subunits share a similarity of 82% and have a high capacity to form a thermodynamically stable dyad structure that is, to our knowledge, the longest ever described in any satellite monomer. Analysis of divergences between inversely oriented subunits shows a tendency to a further reduction in similarity between them. Except in its centromeric localization, the TBREV satellite does not show similarity to other known Tribolium satellites, either in nucleotide sequence or in monomer length and complexity. However, TBREV shares common features of other Tribolium satellites that might be under functional constraints: nonconstant rate of evolution along the monomer sequence, short inverted repeats in the vicinity of an A+T tract, nonrandom distribution of A or T >/=3 tracts, and CENP-B box-like motifs. Although long inverted subunits might reinforce structural characteristics of the satellite monomer, their nucleotide sequence does not seem to be under constraints in order to preserve the dyad structure.

HETEROZYGOTIC TWINNING IN A CASE OF FEMALE VESICOURETHRAL DUPLICATION

A 45-day-old female born at term after a normal pregnancy was referred for a urogenital malformation. Physical examination demonstrated normal vaginal introitus, urethra and labia minora. The upper part of the left labium presented as a 6 3 cm cylindrical mass and a clitoris-like structure with an accessory urethra located at the base. The anus was normally located (fig. 1). Blood, urine, renal function and hormone stimulation analyses were normal, and karyotype was 46,XX. Abdominal ultrasonography showed a normal right kidney and a hypoplastic ectopic left kidney with 2 bladders. The uterus and ovaries were normal. Retrograde cystourethrogram through the orthotopic urethra filled a bladder and induced grade II vesicoureteral reflux to the right kidney. That performed through the ectopic urethral meatus filled a second bladder located posterolaterally to the first one and induced vesicoureteral reflux to an ectopic left kidney. Cystoscopy confirmed 2 normal appearing bladders lined by normal mucosa, each receiving a corresponding ureter. Both urethras were also normal. At surgery 2 completely independent bladders were found together with an ectopic hypoplastic kidney, bicornuate uterus, 2 ovaries, a 36 cm long cecal prolongation resembling a mega-appendix and 1 vas deferens. The mega-appendix, left hypoplastic kidney, bladder, ectopic urethra and vas deferens were removed. No rudimentary gonadal tissue or testis was identified. Finally, the pubic mass was excised and vulvoplasty was performed. Pathological studies determined that the removed urethra was surrounded by prostatic tissue into which a blind ending vas deferens opened (fig. 2). Examination of the pubic mass revealed a chondrolipoma. Molecular studies for gender investigation were performed. Genomic DNA was extracted from paraffin blocks of kidney tissue, clitoris and vas deferens taken during surgery. DNA analysis was performed using polymerase chain reaction. Amplified products were electrophoresed on acrylamide gel and visualized using silver staining. Four of the loci tested on chromosomes 3, 9, 12 and 21 demonstrated different alleles, indicating the presence of 2 diploid genomes. Thus, haplotyping showed the heterozygotic origin of both duplicated elements. Fluorescent in situ hybridization was performed using an X centromere probe DX21 and Y cocktail probe but the results could not confirm 2 different genders. DISCUSSION

Bi-directional duplex promoters with duplicated enhancers significantly increase transgene expression in grape and tobacco.

Novel bi-directional duplex promoters (BDDP) were constructed by placing two identical core promoters divergently on both upstream and downstream sides of their duplicated enhancer elements. Estimates of promoter function were obtained by creating versions of CaMV 35S and CsVMV BDDPs that contained reporter marker genes encoding beta-glucuronidase (GUS) and enhanced green fluorescent protein (EGFP) interchangeably linked either to the upstream or downstream core promoters. GUS was used for quantitative analysis of promoter function, whereas, EGFP allowed visual qualitative evaluation. In addition, the GUS and EGFP genes placed in downstream positions were modified by translational fusion with neomycin phosphotransferase (NPTII) to allow simultaneous monitoring of promoter activity and selection of stable transformants. These versions of BDDP were compared with each other and with equivalent unidirectional constructs by evaluating their expression in grape and tobacco. For 35S promoter constructs tested in grape somatic embryos (SE), BDDP exhibited transient GUS expression 206- and 300-fold greater in downstream and upstream configurations, respectively, compared to a unidirectional 35S core promoter. Compared with a unidirectional double enhanced 35S promoter, BDDPs exhibited 0.5- and 3-fold increased GUS expression from downstream and upstream core promoters, respectively. The same differences in expression levels determined quantitatively with GUS were distinguished qualitatively with EGFP. Constructs using CsVMV core promoters yielded results relative to those obtained with 35S promoter. For example, the upstream BDDP CsVMV core promoter provided a 200-fold increase in GUS expression compared to a unidirectional core promoter. However, CsVMV promoter was found to have higher promoter activity than 35S promoter in both BDDP and unidirectional constructs. Incorporation of an additional duplicated enhancer element to BDDPs resulted in increased expression. For example, a 35S BDDP with two divergently arranged duplicated enhancer elements resulted in over a 6-fold increase in GUS expression in stably transformed tobacco plants compared to a BDDP with one duplicated enhancer element. Data demonstrate that BDDP composed of divergently-arranged core promoters separated by duplicated enhancers, all derived from a single promoter sequence, can be used to significantly enhance transgene expression and to direct synchronized expression of multiple transgenes.

Concerted evolution between duplicated genetic elements in Helicobacter pylori

The Helicobacter pylori genome includes a family of outer membrane proteins (OMPs) with substantial N and C-terminal identity. To better understand their evolution, the nucleotide sequences for two members, babA and babB, were determined from a worldwide group of 23 strains. The geographic origin of each strain was found to be the major determinant of phylogenetic structure, with strains of Eastern and Western origin showing greatest divergence. For strains 96-10 (Japan) and 96-74 (USA), the 5′ regions of babB are replaced with babA sequences, demonstrating that recombination occurs between the two loci. babA and babB have nearly equivalent variation in nucleotide and amino acid identity, and frequencies of synonymous and non-synonymous substitutions. Both genes have segmental conservation but within the 3′ segment, substitution patterns are nearly identical. Although babA and babB 5′ and midregion segment phylogenies show strong interstrain similarity, the 3′ segments show strong intrastrain similarity, indicative of concerted evolution. Within these 3′ segments, the lower intrastrain than interstrain frequencies of nucleotide substitutions, which are below mean background H. pylori substitution frequencies, indicate selection against intrastrain diversification. Since babA/ babB gene conversions likely underlie the concerted evolution of the 3′ segments, in an experimental system, we demonstrate that gene conversions can frequently (10 −3) occur in H. pylori. That these events are recA-dependent and DNase-resistant indicates their likely cause is intragenomic recombination.

Homeotic transformation of branchial arch identity after Hoxa2 overexpression.

Overexpression of Hoxa2 in the chick first branchial arch leads to a transformation of first arch cartilages, such as Meckel's and the quadrate, into second arch elements, such as the tongue skeleton. These duplicated elements are fused to the original in a similar manner to that seen in the Hoxa2 knockout, where the reverse transformation of second to first arch morphology is observed. This confirms the role of Hoxa2 as a selector gene specifying second arch fate. When first arch neural crest alone is targeted, first arch elements are lost, but the Hoxa2-expressing crest is unable to develop into second arch elements. This is not due to Hoxa2 preventing differentiation of cartilages. Upregulation of a second arch marker in the first arch, and homeotic transformation of cartilage elements is only produced after global Hoxa2 overexpression in the crest and the surrounding tissue. Thus, although the neural crest appears to contain some patterning information, it needs to read cues from the environment to form a coordinated pattern. Hoxa2 appears to exert its effect during differentiation of the cartilage elements in the branchial arches, rather than during crest migration, implying that pattern is determined quite late in development.

Broad-Range Bacteriophage Resistance in Streptococcus thermophilus by Insertional Mutagenesis

Streptococcus thermophilus is a lactic acid bacterium used in industrial milk fermentation. To obtain phage-resistant starters, S. thermophilus strain Sfi1 was submitted to mutagenesis with the thermolabile insertional vector pG+host9:ISS1 followed by a challenge with the lytic S. thermophilus phage Sfi19. Vector insertions into four distinct sites led to a phage-resistance phenotype. Three mutants were characterized further. They were protected against the homologous challenging phage and 14 heterologous phages. All three mutants adsorbed phages. No intracellular phage DNA synthesis was observed in mutants R7 and R71, while mutant R24 showed a delayed and diminished phage DNA synthesis compared to the parental Sfi1 strain. In mutant R7 a short deletion occurred next to the insertion site which removed the upstream sequences and the 15 initial codons from orf 394, encoding a likely transmembrane protein. Analogy with other phage systems suggests an involvement of this protein in the phage DNA injection process. In mutant R24 the vector was inserted into orf 269 predicting an oxido-reductase. When the vector sequence was removed via homologous recombination across the duplicated insertion elements, mutant R24 returned to the phage susceptibility of the parental strain. This observation suggested that inactivation of orf 269 was not crucial for the resistance phenotype. A gene encoding a likely restriction subunit of a type I restriction-modification system was located directly downstream of the insertion site in mutant R24. hsdM and hsdS genes encoding the modification and specificity subunits of a type I R-M system and biological evidence for an active R-M system were detected in strain Sfi1, suggesting involvement of a type I R-M system in the resistance phenotype of R24.

Human immunodeficiency virus type 1 genome activation induced by human T-cell leukemia virus type 1 Tax protein is through cooperation of NF-kappaB and Tat.

For productive replication of human immunodeficiency virus type 1 (HIV-1) in host cells, the viral genome-encoded transactivator Tat and several cellular transcription factors are required for efficient viral gene transcription. However, it remains unclear how the viral genome initiates transcription before Tat is transcribed or when Tat is at suboptimal levels. Here, we utilized the human T-cell leukemia type 1 Tax protein as a molecular tool to investigate the mechanism of viral gene transcription that initiates the early phase of infection of HIV-1. Tax alone does not significantly increase the activity of HIV-1 long terminal repeat (LTR) in T lymphocytes, but it markedly enhanced the replication of an infectious HIV-1 provirus with a truncated nef gene. This enhancement is preferentially mediated by the cooperation of Tax and Tat which is dependent on TAR and duplicated kappaB cis elements of the HIV-1 LTR as well as the NF-kappaB activation domain of Tax. Furthermore, phorbol myristate acetate and membrane-targeted HIV-1 Nef also enhanced the LTR activity in the presence of Tat in the TAR- and kappaB cis element-dependent manner. These data suggest that activated NF-kappaB can functionally interact with a suboptimal amount of Tat and the HIV-1 LTR for efficient initiation of viral gene transcription.

Factors affecting ectopic gene conversion in mice.

Duplicated genes and repetitive sequences are distributed throughout the genomes of complex organisms. The homology between related sequences can promote nonallelic (ectopic) recombination, including gene conversion and reciprocal exchange. Resolution of these events can result in translocations, deletions, or other harmful rearrangements. In yeast, ectopic recombination between sequences on nonhomologous chromosomes occurs at high frequency. Because the mammalian genome is replete with duplicated sequences and repetitive elements, high levels of ectopic exchange would cause aneuploidy and genome instability. To understand the factors regulating ectopic recombination in mice, we evaluated the effects of homology length on gene conversion between unlinked sequences in the male germline. Previously, we found high levels of gene conversion between lacZ transgenes containing 2557 bp of homology. We report here that genetic background can play a major role in ectopic recombination; frequency of gene conversion was reduced by more than an order of magnitude by transferring the transgenes from a CF1 strain background to C57BL/6J. Additionally, conversion rates decreased as the homology length decreased. Sequences sharing 1214 bp of sequence identity underwent ectopic conversion less frequently than a pair sharing 2557 bp of identity, while 624 bp was insufficient to catalyze gene conversion at significant levels. These results suggest that the germline recombination machinery in mammals has evolved in a way that prevents high levels of ectopic recombination between smaller classes of repetitive sequences, such as the Alu family. Additionally, genomic location appeared to influence the availability of sequences for ectopic recombination.

Reliable nonlinear control system design using duplicated control elements

Reliable L2 gain bounding (i.e., H∞) controllers for nonlinear systems are designed by using redundant control elements. One sensor and one actuator are duplicated, and the resulting closed-loop system is reliable with respect to both the single contingency case and the primary contingency case. The design procedures for reliable controllers are developed by using the Hamilton–Jacobi inequalities from nonlinear H∞ control theory. Linear reliable controller design methods are also obtained by restricting the proposed nonlinear methods to the linear case, and the linear methods are found to be less conservative than existing methods for linear reliable controller design. Examples are given to illustrate the design procedures for both linear and nonlinear reliable controllers and the advantages of the proposed linear method over existing ones. © 1997 by John Wiley & Sons, Ltd.

Reliable nonlinear control system design using duplicated control elements

Reliable L2 gain bounding (i.e., H∞) controllers for nonlinear systems are designed by using redundant control elements. One sensor and one actuator are duplicated, and the resulting closed-loop system is reliable with respect to both the single contingency case and the primary contingency case. The design procedures for reliable controllers are developed by using the Hamilton–Jacobi inequalities from nonlinear H∞ control theory. Linear reliable controller design methods are also obtained by restricting the proposed nonlinear methods to the linear case, and the linear methods are found to be less conservative than existing methods for linear reliable controller design. Examples are given to illustrate the design procedures for both linear and nonlinear reliable controllers and the advantages of the proposed linear method over existing ones. © 1997 by John Wiley & Sons, Ltd.

Opposite orientations of an inverted duplication and allelic variation at the mouse agouti locus.

The mouse agouti protein is a paracrine signaling molecule that causes yellow pigment synthesis. A pale ventral coloration distinguishes the light-bellied agouti (AW) from the agouti (A) allele, and is caused by expression of ventral-specific mRNA isoforms with a unique 5' untranslated exon. Molecular cloning demonstrates this ventral-specific exon lies within a 3.1-kb element that is duplicated in the opposite orientation 15-kb upstream to produce an interrupted palindrome and that similarity between the duplicated elements has been maintained by gene conversion. Orientation of the palindrome is reversed in A compared to AW, which suggests that mutation from one allele to the other is caused by intrachromosomal homologous recombination mediated by sequences within the duplicated elements. Analysis of 15 inbred strains of laboratory and wild-derived mice with Southern hybridization probes and closely linked microsatellite markers suggests six haplotype groups: one typical for most strains that carry AW (129/SvJ, LP/J, CE/J, CAST/Ei), one typical for most strains that carry A (Balb/cJ, CBA/J, FVB/N, PERA/Rk, RBB/Dn); and four that are atypical (MOLC/Rk, MOLG/Dn, PERA/Ei, PERC/Ei, SPRET/Ei, RBA/Dn). Our results suggest a model for molecular evolution of the agouti locus in which homologous recombination can produce a reversible switch in allelic identity.

Analysis of Tn5 inversion events in Escherichia coli plasmids.

The ability of the bacterial transposon Tn5 to undergo sequence inversion in Rec+ Escherichia coli cells as a result of recombination between its duplicated IS50 elements was examined using specially designed plasmid constructs. Surprisingly, recombination events in the IS50 elements that led to crossover and therefore Tn5 inversion could be detected at a frequency of only 10(-5). This was approximately an order of magnitude lower than the frequency of IS50 recombination that led to conversion events (i.e. non-reciprocal recombination) without crossover, and at least two orders of magnitude lower than the frequency of intermolecular recombination between IS50 elements on two different plasmids. These rare conversion and inversion events in Tn5 appeared to be due to intramolecular recombination and not simply to multiple rounds of reciprocal crossing over, since the heterodimeric intermediates that would be generated during the latter process could be readily isolated but were shown to yield a completely different set of plasmid products upon resolution.

A Symphony of Government Design: Imitation in State Constitutions on the Southern Frontier, 1812-1845

The original constitutions of six Southern frontier states are compared: Louisiana's (1812), Mississippi's (1817), Alabama's (1819), Arkansas's (1836), Florida's (1839), and Texas's (1845). Identical or similar elements are examined, and the historical circumstances leading each constitutional convention to adopt this group of provisions are recounted. The duplicated elements include some of the structures of the three branches of government, some individual rights, the methods of choosing seats of government, adaptations to epidemic disease, and means of enforcing fiscal accountability. Primary sources are the constitutions, the constitutional convention journals, territorial papers, and some legislative records, letters, and newspapers. This historical study of constitutional convergence conveniently summarizes parts of antebellum Southern frontier history and also examines the diffusion of a constitutional core of techniques of self-government.

Local transposition of P elements in Drosophila melanogaster and recombination between duplicated elements using a site-specific recombinase.

The transposase source delta 2-3(99B) was used to mobilize a P element located at sites on chromosomes X, 2 and 3. The transposition event most frequently recovered was a chromosome with two copies of the P element at or near the original site of insertion. These were easily recognized because the P element carried a hypomorphic white gene with a dosage dependent phenotype; flies with two copies of the gene have darker eyes than flies with one copy. The P element also carried direct repeats of the recombination target (FRT) for the FLP site-specific recombinase. The synthesis of FLP in these flies caused excision of the FRT-flanked white gene. Because the two white copies excised independently, patches of eye tissue with different levels of pigmentation were produced. Thus, the presence of two copies of the FRT-flanked white gene could be verified. When the P elements lay in the same orientation, FLP-mediated recombination between the FRTs on separated elements produced deficiencies and duplications of the flanked region. When P elements were inverted, the predominant consequence of FLP-catalyzed recombination between the inverted elements was the formation of dicentric chromosomes and acentric fragments as a result of unequal sister chromatid exchange.