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PubMed1986

The heterochromatin of grasshoppers from the Caledia captiva species complex. I. Sequence evolution and conservation in a highly repeated DNA family.

The restriction enzyme TaqI digests 0.2% of the genomic DNA from the grasshopper Caledia captiva to a family of sequences 168 bp in length (length of consensus sequence). The sequence variation of this "Taq family" of repeat units was examined among four races from C. captiva to assay the pattern of evolution within this highly repeated DNA. The Taq-family repeats are located in C-banded heterochromatin on at least one member of each homologous pair of chromosomes; the locations range from centromeric to telomeric. Thirty-nine cloned repeats isolated from two population 1A individuals along with 11 clones from seven populations taken from three of the races demonstrated sequence variation at 72 positions. Pairwise comparisons of the cloned repeats, both within an individual and between different races, indicate that levels of intraspecific divergence, as measured by reproductive incompatibility, do not correlate with sequence divergence among the 168-bp repeats. A number of subsequences within the repeat remain unchanged among all 50 clones; the longest of these is 18 bp. That the same 18-bp subsequence is present in all clones examined is a finding that departs significantly (P less than 0.01) from what would be expected to occur at random. Two other cloned repeats, from a reproductively isolated race of C. captiva, have sequences that show 56% identity with this 18-bp conserved region. An analysis showed that the frequency of occurrence of an RsaI recognition site within the 168-bp repeat in the entire Taq family agreed with that found in the cloned sequences. These data, along with a partial sequence for the entire Taq family obtained by sequencing uncloned repeats, suggest that the consensus sequence from the cloned copies is representative of this highly repeated family and is not a biased sample resulting from the cloning procedure. The 18-bp conserved sequence is part of a 42-bp sequence that possesses dyad symmetry typical of protein-binding sites. We speculate that this may be significant in the evolution of the Taq family of sequences.

Animals↗

PubMedDate not supplied

Effects of rRNA gene copy number and nucleolar variation on early development: inhibition of gastrulation in rDNA-deficient chick embryos.

Because of their structural and catalytic functions during protein synthesis, the 18S, 5.8S, and 28S ribosomal RNAs (rRNAs) are essential for the support of differentiation, development, and growth. The genes encoding these RNAs are present in high copy number in all eukaryotes. Although there is evidence for the existence of variation for rRNA gene copy number within higher vertebrate species, there is little knowledge concerning the effects of such variation, especially reductions, on development and viability of homeothermic vertebrates. The main objective of this study was to determine the developmental potential of chick embryos containing defined deficiencies for rRNA gene copy number in order to assess the contribution of rDNA cluster size variation to embryonic mortality in homeothermic vertebrates. This was achieved by studying a strain of chickens containing nucleolar size polymorphisms that reflect rDNA cluster size polymorphisms. Embryos exhibiting a nucleolar phenotype of one large and one very small nucleolus (Pp) are heterozygous for a reduced rDNA cluster (+/p1) and were shown in the present study to contain about 66% of the complement of rRNA genes in normal individuals (+/+) that show two large equal-sized nucleoli (PP). The +/p1 embryos were found to develop and grow normally. Embryos exhibiting a nucleolar phenotype of two very small nucleoli (pp) are homozygous for the rDNA-deficient cluster (p1/p1) and contained about 45% of the normal rDNA complement of genes. These p1/p1 embryos were arrested in their development during early gastrulation. They exhibited a characteristic morphology consisting of a dorsal invagination that was strikingly different from the primitive streak formed in +/+ and +/p1 individuals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Evolutionary transience of hypervariable minisatellites in man and the primates.

Using PCR, two minisatellite loci showing extreme repeat-unit copy-number variation in humans have been characterized in great apes and monkeys. In contrast to humans, minisatellite locus MS32 is monomorphic with only 3-4 diverged repeat units in great apes, Old World and New World monkeys, this organization presumably representing the relatively stable ancestral precursor state of the human hypervariable locus. Similarly, minisatellite MS1 shows extreme repeat-copy-number variability in man compared with low copy number and minimal variability in great apes. Analysis of variant repeat units shows that the 5' and 3' regions of MS1 are relatively stable in great apes and man, and that variability in man is confined to the central region of the minisatellite. In contrast to the great apes, MS1 is highly variable in Old World monkeys. These results, as well as computer simulations of minisatellite evolution based on known mutation rates, show that short minisatellites are stable within the genome, and that the degree of polymorphism at a given locus can change dramatically over a short period of evolutionary time. The ability of hypervariable minisatellites to detect highly informative loci by cross-species hybridization is therefore largely unpredictable.

Animals↗

PubMed1986

The silkmoth late chorion locus. II. Gradients of gene conversion in two paired multigene families.

The late chorion locus of Bombyx mori is composed of two multigene families arranged as divergently oriented pairs irregularly spaced over 140 X 10(3) bases of DNA. The average sequence homology is 91% for the 15 members of each family. DNA sequence analysis reveals: that most of the sequence variants found in individual members of a family are shared by two or more members of that family; that family members sharing a particular variant are scattered throughout the locus; and adjacent variants in individual genes are often shared by different subsets of family members. The large number of shared variants scored and their distribution is most simply explained by numerous sequence transfers similar to gene conversions. These sequence transfers are not uniformly distributed along each gene pair. Sequence transfer is highest near the 3' end of each gene and lowest in the common 5' region between the divergent genes. A model is presented that explains these gradients by assuming that the events leading to gene conversion preferentially initiate in a simple-sequence DNA repeat. The resulting heteroduplexes extend to distances influenced by features of the sequence affecting their stability. The simple-sequence DNA is part of the major exon in both gene families and encodes tandem copies of the sequence Cys-Gly-Gly and Cys-Gly. Striking identity in the precise pattern of codon biases of these repeated sequences in the two families suggests that repeated sequence transfers occur also between families in this simple-sequence region.

Animals↗

PubMed1991

Organization of DNA sequences highly repeated in tandem in rice genomes.

Digestion of the total genomic DNA from rice Oryza sativa L. cv. C5924 with EcoRI generated an intense band of a DNA fragment of about 0.36 kb long. The DNA fragment cloned into pUC19 was used to hybridize with the total rice genomic DNA partially digested with EcoRI. A ladder of bands of DNA fragments with multiplied length of 0.36 kb was observed, demonstrating that this sequence occurs in tandem in the genome. The copy number of the sequence estimated by dot blot hybridization analysis was 2000-3000 copies per haploid genome from callus or seedling of C5924. This sequence was present in other O. sativa cultivars, such as Sasanishiki in 700-900 copies, Koshihikari in 3400-4300, and Nipponbare in 4600-6000 copies. Another rice species, O. glaberrima, also had this sequence in 540-680 copies, but four lines of foxtail millet had none. The DNA fragments containing the repeated sequences in Nipponbare were then cloned into lambda EMBL3, and sequences of nine units consecutively repeated and an AT-rich sequence connected with them in a phage clone could be determined. Each repeating unit showed sequence divergency mostly by substitution of bases in a range from 3% to 7%, when compared with a 355-bp consensus sequence. Analyses of the substituted bases indicate that these are due to spontaneous mutations which occurred at random, after reiteration of a unit sequence by unequal crossing over events. Gene conversion within the repeated sequences might have further diversified their sequences.

Base Sequence↗

PubMed1996

Is point mutagenesis a mechanism for antigenic variation in Trypanosoma brucei?

Antigenic variation in African trypanosomes proceeds by switching between different variant surface glycoprotein (VSG) molecules, whose extensive epitope differences enable evasion of antibody responses. Each trypanosome has approximately 1000 basic copy VSG genes inside chromosomes and a subset located at telomeres. Switching usually involves different individual basic copy genes being duplicated, as an expression linked copy, into a transcriptionally active site. In a few cases expression linked copies with a number of point mutations have been observed, leading to the suggestion that point mutagenesis provides another mechanism of antigenic variation. The most extensive example is a VSG gene that is normally activated in the metacyclic population in the tsetse fly, but the point mutations were detected in expression linked copies generated during bloodstream infection, after prolonged growth and selection. It was suggested that particularly telomeric or metacyclic VSG genes might undergo point mutagenesis during expression linked copy formation. To test this we have cloned 3 trypanosomes very soon after they had generated, during mouse infection, expression linked copies of the metacyclic VSG gene ILTat 1.22 and have detected only a single point mutation which is present in one expression linked copy, but not the corresponding basic copy, gene. This mutation does not prevent binding of a neutralizing antibody. Extensive VSG gene point mutagenesis may be a consequence merely of prolonged growth and extensive selection. There is not a single reported case of a point mutated VSG presenting a completely new set of exposed epitopes, suggesting point mutagenesis is unlikely to be an authentic mechanism for antigenic variation.

Animals↗

PubMed1998

Plasma SIV RNA viral load determination by real-time quantification of product generation in reverse transcriptase-polymerase chain reaction.

Internally controlled RT-PCR methods (QC-RT-PCR) for quantification of SIV RNA are effective, but are relatively cumbersome, expensive, and time and labor intensive. For greater throughput and efficiency, we have developed a method for quantification of plasma SIV RNA levels by real-time RT-PCR using the Applied Biosystems Prism 7700 sequence detection system. This assay format allows real-time kinetic analysis of PCR product generation, providing a broad linear dynamic range and ensuring that quantification is based on analysis during the exponential phase of amplification, regardless of the input template copy number. Simultaneous amplification and analysis eliminates any requirement for handling amplified products, increasing throughput and eliminating a potential source of assay contamination. The assay we have developed for quantification of SIV RNA has a nominal threshold sensitivity of 300 copy Eq/ml of plasma, although as little as 10 copy Eq/reaction of SIV RNA template can be detected. The linear dynamic range is in excess of 5 logs. Interassay reproducibility averages 25% (coefficient of variation), based on studies of extraction and analysis of replicate aliquots of the same plasma specimens. The combination of sensitivity, precision, and broad dynamic range allows reliable quantification of viral load even during dynamic phases of SIV infection, such as through the onset and resolution of primary infection, or during treatment with antiretroviral agents. The primer-probe combinations we have developed allow quantification of SIV isolates most commonly used for experimental studies. Availability of this assay should greatly facilitate studies of basic pathogenesis and evaluation of therapeutic and prophylactic approaches in the SIV-infected macaque.

Animals↗

PubMed2004

The amplification model for adaptive mutation: simulations and analysis.

It has been proposed that the lac revertants arising under selective conditions in the Cairns experiment do not arise by stress-induced mutagenesis of stationary phase cells as has been previously assumed. Instead, these revertants may arise within growing clones initiated by cells with a preexisting duplication of the weakly functional lac allele used in this experiment. It is proposed that spontaneous stepwise increases in lac copy number (amplification) allow a progressive improvement in growth. Reversion is made more likely primarily by the resultant increase in the number of mutational targets--more cells with more lac copies. The gene amplification model requires no stress-induced variation in the rate or target specificity of mutation and thus does not violate neo-Darwinian theory. However, it does require that a multistep process of amplification, reversion, and amplification segregation be completed within approximately 20 generations of growth. This work examines the proposed amplification model from a theoretical point of view, formalizing it into a mathematical framework and using this to determine what would be required for the process to occur within the specified period. The analysis assumes no stress-induced change in mutation rate and describes only the growth improvement occurring during the process of amplification and subsequent elimination of excess mutant lac copies. The dynamics of the system are described using Monte Carlo simulations and numerical integration of the deterministic equations governing the system. The results imply that the amplification model can account for the behavior of the system using biologically reasonable parameter values and thus can, in principle, explain Cairnsian adaptive mutation.

Adaptation, Biological↗

PubMed2001

Haplotype variation in a mitochondrial tandem repeat of Norway spruce (Picea abies) populations suggests a serious founder effect during postglacial re-colonization of the western Alps.

Populations from 13 elevational transects of Norway spruce [Picea abies (L.) Karst] across the Alpine range were sampled to elucidate the geographical pattern of genetic variation in relation to postglacial re-colonization and to study elevational effects on haplotypic diversity. We assessed fragment length variation in a tandem repeat region of the mitochondrial (mt) nad1 intron 2. This maternally inherited genetic marker is suited to infer migration as it is dispersed by seed only. A total of 10 haplotypes was found, most of which were due to repeat copy number variation. An analysis of molecular variance (amova) showed that overall population differentiation was high (F(ST)=0.41), and it revealed a significant differentiation between monomorphic western and moderately to highly variable eastern Alpine populations. This phylogeographic pattern may be explained by a founder effect during postglacial re-colonization. An early arriving haplotype, assumed to originate from a western Carpathian refugium, could expand into suitable habitats, reducing the chances for establishment of subsequently arriving haplotypes. On the other hand, the high variation in populations within an Italian transect of the south-eastern Alps may be the consequence of merging migration pathways from and close distance to putative glacial refugia, most likely those assumed in the Carpathian mountains and on the Balkan peninsula or possibly in the central plains of Italy. An effect of elevation on haplotypic diversity was not evident, though a low, but significant, partition of total genetic variation was attributed to among-population variation in one Italian transect. Various factors, such as vertical seed dispersal and forest management, may account for blurring an otherwise established pattern of genetic variation on a small geographical scale.

Analysis of Variance↗

PubMed2001

Equine infectious anemia virus genomic evolution in progressor and nonprogressor ponies.

A primary mechanism of lentivirus persistence is the ability of these viruses to evolve in response to biological and immunological selective pressures with a remarkable array of genetic and antigenic variations that constitute a perpetual natural experiment in genetic engineering. A widely accepted paradigm of lentivirus evolution is that the rate of genetic variation is correlated directly with the levels of virus replication: the greater the viral replication, the more opportunities that exist for genetic modifications and selection of viral variants. To test this hypothesis directly, we examined the patterns of equine infectious anemia virus (EIAV) envelope variation during a 2.5-year period in experimentally infected ponies that differed markedly in clinical progression and in steady-state levels of viral replication as indicated by plasma virus genomic RNA assays. The results of these comprehensive studies revealed for the first time similar extents of envelope gp90 variation in persistently infected ponies regardless of the number of disease cycles (one to six) and viremia during chronic disease. The extent of envelope variation was also independent of the apparent steady-state levels of virus replication during long-term asymptomatic infection, varying from undetectable to 10(5) genomic RNA copies per ml of plasma. In addition, the data confirmed the evolution of distinct virus populations (genomic quasispecies) associated with sequential febrile episodes during acute and chronic EIA and demonstrated for the first time ongoing envelope variation during long-term asymptomatic infections. Finally, comparison of the rates of evolution of the previously defined EIAV gp90 variable domains demonstrated distinct differences in the rates of nucleotide and amino acid sequence variation, presumably reflecting differences in the ability of different envelope domains to respond to immune or other biological selection pressures. Thus, these data suggest that EIAV variation can be associated predominantly with ongoing low levels of virus replication and selection in target tissues, even in the absence of substantial levels of plasma viremia, and that envelope variation continues during all stages of persistent infection as the virus successfully avoids clearance by host defense mechanisms.

Acute Disease↗

PubMed1990

Alignment of U3 region sequences of mammalian type C viruses: identification of highly conserved motifs and implications for enhancer design.

We aligned published sequences for the U3 region of 35 type C mammalian retroviruses. The alignment reveals that certain sequence motifs within the U3 region are strikingly conserved. A number of these motifs correspond to previously identified sites. In particular, we found that the enhancer region of most of the viruses examined contains a binding site for leukemia virus factor b, a viral corelike element, the consensus motif for nuclear factor 1, and the glucocorticoid response element. Most viruses containing more than one copy of enhancer sequences include these binding sites in both copies of the repeat. We consider this set of binding sites to constitute a framework for the enhancers of this set of viruses. Other highly conserved motifs in the U3 region include the retrovirus inverted repeat sequence, a negative regulatory element, and the CCAAT and TATA boxes. In addition, we identified two novel motifs in the promoter region that were exceptionally highly conserved but have not been previously described.

Animals↗

PubMed1995

Different evolutionary behaviour of P element subfamilies: M-type and O-type elements in Drosophila bifasciata and D. imaii.

Distribution and variation of two P-element subfamilies designated M-type and O-type elements were investigated in Drosophila bifasciata (Db) and its relatives. PCR screening revealed that full-sized and internally deleted elements of both types occur in three geographic Db strains and in the related species, D. imaii (Di). Molecular analyses indicate differences in the evolutionary behaviour of the two P-element types. Internally deleted M-type elements fall into two size classes present in all three Db strains. In contrast, internally deleted O-type elements vary between the strains in number and length. With respect to genomic location, M-type elements seem to be restricted to conserved euchromatic sites, whereas the positions of O-type elements appear to be geographically variable. In one strain of Db (Italy), O-type elements seem to accumulate in the heterochromatin. Sequencing of a 397-bp segment shows intra- and interspecific divergence of M-type elements. In a 452-bp segment of the O-type elements, no substitutions were found, neither within nor between species. This finding suggests recent introgression of O-type elements via hybridization between Db and Di. Sequence identity and variation in chromosomal locations among different copies imply that O-type elements are transpositionally active. For M-type elements, genomic mobility cannot be proved. In a survey of several other taxa, no O-type-related sequences were detected so far. Therefore, the origin of the O-type subfamily remains unknown, whereas the source of M-type elements can be traced back to the genus Scaptomyza.

Animals↗

PubMed1997

Genomic structure and organization of kringles type 3 to 10 of the apolipoprotein(a) gene in 6q26-27.

Apolipoprotein(a) [apo(a)] is a highly polymorphic glycoprotein covalently linked to the apolipoprotein B-100 of LDL in a particle called lipoprotein(a) [Lp(a)]. High plasma levels of Lp(a) are associated with coronary as well as peripheral atherosclerosis. Plasma levels of Lp(a) show a remarkable variation ranging from 0.1 mg/dl to over 100 mg/dl. The apo(a) gene shows a size polymorphism which resides in the variable number of kringle domains which resemble plasminogen kringle IV. Ten different types of kringle IV repeats have been described, nine of which (kringle IV type 1 and type 3-10) are each supposed to be present in a single copy. The other kringles, namely kringle IV type 2 repeats, vary in number from 3 to 42 between apo(a) alleles and form the basis for the apo(a) size polymorphism. Although an inverse relationship has been observed between the number of kringle type 2 repeats and plasma levels of Lp(a), there are exceptions to this general finding. Indeed, several individuals have been described with similar apo(a) size alleles but very different plasma levels of Lp(a). Genetic studies have linked these differences to the apo(a) locus on 6q26-27, outlining the importance, besides the kringle type 2 repeats, of other regions of the apo(a) gene in contributing to the interindividual differences in the plasma concentration of Lp(a). One of the candidate regions is represented by the non-repeated type-3 to type-10 kringles which are invariably present in each apo(a) allele and whose structural integrity is playing a critical role in the correct assembly of the Lp(a) particle. Biochemical studies with recombinant wild type and mutagenized apo(a) cDNAs with several alterations of the non-repeated kringles have well documented this latter point. As a starting point to search for genetic variations in these kringles associated with different levels of Lp(a), we are presenting the genome organization of type-3 to 10 kringle along with specific PCR primers for easy analysis from genomic DNA. Restriction as well as partial sequencing analyses of the type-3 to 10 kringles region has also provided interesting clues as to the different evolutionary origin of these types of kringle with respect to the polymorphic type-2 kringles.

Apolipoproteins A↗

PubMed2004

Insertion bias and purifying selection of retrotransposons in the Arabidopsis thaliana genome.

BACKGROUND: Genome evolution and size variation in multicellular organisms are profoundly influenced by the activity of retrotransposons. In higher eukaryotes with compact genomes retrotransposons are found in lower copy numbers than in larger genomes, which could be due to either suppression of transposition or to elimination of insertions, and are non-randomly distributed along the chromosomes. The evolutionary mechanisms constraining retrotransposon copy number and chromosomal distribution are still poorly understood. RESULTS: I investigated the evolutionary dynamics of long terminal repeat (LTR)-retrotransposons in the compact Arabidopsis thaliana genome, using an automated method for obtaining genome-wide, age and physical distribution profiles for different groups of elements, and then comparing the distributions of young and old insertions. Elements of the Pseudoviridae family insert randomly along the chromosomes and have been recently active, but insertions tend to be lost from euchromatic regions where they are less likely to fix, with a half-life estimated at approximately 470,000 years. In contrast, members of the Metaviridae (particularly Athila) preferentially target heterochromatin, and were more active in the past. CONCLUSION: Diverse evolutionary mechanisms have constrained both the copy number and chromosomal distribution of retrotransposons within a single genome. In A. thaliana, their non-random genomic distribution is due to both selection against insertions in euchromatin and preferential targeting of heterochromatin. Constant turnover of euchromatic insertions and a decline in activity for the elements that target heterochromatin have both limited the contribution of retrotransposon DNA to genome size expansion in A. thaliana.

Arabidopsis↗

PubMed1990

A retroposon in the 5' flank of a Trypanosoma brucei VSG gene lacks insertional terminal repeats.

A retroposon-like repeated sequence, ingi, occurs in high copy number in the genome of Trypanosoma brucei brucei. An ingi is present in the 5' flank of the 5C gene, an intrachromosomal IsTat 1.5 variant surface glycoprotein (VSG) gene family member. The 5' end of the ingi is located 22 bp upstream of the putative VSG start codon and the ingi open reading frame is in the opposite orientation to that of the VSG gene. The termini of the ingi are not flanked by a short repeat sequence and there are no sequences upstream of the ingi insertion which are homologous to the 5' flanking sequence of other 5 VSG gene family members. Thus, it appears that recombination and/or gene conversion between two ingi sequences may have eliminated the original 5C gene flanking sequence. Similar events may also have occurred with all but one previously reported ingi.

Amino Acid Sequence↗

PubMed1989

Molecular population genetics of mtDNA size variation in crickets.

Nucleotide sequence analysis of a region of cricket (Gryllus firmus) mtDNA showing discrete length variation revealed tandemly repeated sequences 220 base pairs (bp) in length. The repeats consist of 206 bp sequences bounded by the dyad symmetric sequence 5'GGGGGCATGCCCCC3'. The sequence data showed that mtDNA size variation in this species is due to variation in the number of copies of tandem repeats. Southern blot analysis was used to document the frequency of crickets heteroplasmic for two or more different-sized mtDNAs. In New England populations of G. firmus and a close relative Gryllus pennsylvanicus approximately 60% of the former and 45% of the latter were heteroplasmic. From densitometry of autoradiographs the frequencies of mtDNA size classes were determined for the population samples and are shown to very different in the two species. However, in populations where hybridization between the two species has occurred, the frequencies of size classes and cytoplasmic genotypes in each species' distinct mtDNA lineage were shifted in a manner suggesting nuclear-cytoplasmic interactions. The data were applied to reported diversity indices and hierarchical statistics. The hierarchical statistics indicated that the greatest proportion of variation for mtDNA size was due to variation among individuals in their cytoplasmic genotypes (heteroplasmic or homoplasmic state). The diversity indices were used to estimate a per-generation mutation rate for size variants of 10(-4). The data are discussed in light of the relationship between genetic drift and mutation in maintaining variation for mtDNA size.

Animals↗

PubMed2004

[Structure and expression of the F6.2 gene in Chironomus thummi and other Chironomus species].

A full-length copy of the F6.2 gene from the tissue-specific BRa locus of the Chironomus thummi chromosome IV was isolated and analyzed. The gene contains two exons (715 and 644 bp, respectively) and one 172-bp intron. The data of the RT-PCR analysis demonstrated that F6.2 was transcriptionally active at different developmental stages of Chironomus thummi and at least in the last larval stage of C. dorsalis. The distribution of the F6.2 gene among 42 species of Chironomus, as well as among two other genera of the family Chironomidae was examined by means of PCR. The F6.2 sequence was found in 34 Chironomus species. Using in situ hybridization, three species were analyzed for the presence of the F6.2 homologous sequences. In five species, the sequence of the F6.2 PCR product was determined. In these species, the intron size polymorphism caused by the variation of the number of the intron-forming repeats was observed. The data obtained provided evaluation of the F6.2 distribution among the genus Chironomus.

Amino Acid Sequence↗

PubMed1998

Genotyping of hepatitis E virus in clinical specimens by restriction endonuclease analysis.

The genomic variability of hepatitis E virus (HEV) was examined by restriction endonuclease analysis (REA) of four genomic cDNA copies comprising a 499 bp segment of the putative polymerase gene, a 264 bp segment of the helicase gene, and two, 680 bp and 448 bp, segments of the capsid gene. Analysis of the deduced restriction sites of all 27 HEV sequences currently available in the GenBank, and digestion of reverse-transcribed and nested PCR amplified segments obtained from six Nepali isolates were used to devise and test a REA genotyping assay. The assay allowed easy discrimination between the Mexico and Asian genotypes, and the classification of the Asian genotypes into three, or perhaps four subgenotypes. In addition, endonucleases identifiers of individual isolate or clusters of isolates were found. This assay permits rapid identification of a large number of HEV isolates directly from clinical specimens for studies on the molecular epidemiology and evolution of HEV.

DNA Restriction Enzymes↗