A genome-wide association study identifies two loci associated with heart failure due to dilated cardiomyopathy

AIMS

Dilated cardiomyopathy (DCM) is a major cause of heart failure with a high familial recurrence risk. So far, the genetics of DCM remains largely unresolved. We conducted the first genome-wide association study (GWAS) to identify loci contributing to sporadic DCM.

METHODS AND RESULTS

One thousand one hundred and seventy-nine DCM patients and 1108 controls contributed to the discovery phase. Pools of DNA stratified on disease status, population, age, and gender were constituted and used for testing association of DCM with 517 382 single nucleotide polymorphisms (SNPs). Three DCM-associated SNPs were confirmed by individual genotyping (P < 5.0 10(-7)), and two of them, rs10927875 and rs2234962, were replicated in independent samples (1165 DCM patients and 1302 controls), with P-values of 0.002 and 0.009, respectively. rs10927875 maps to a region on chromosome 1p36.13 which encompasses several genes among which HSPB7 has been formerly suggested to be implicated in DCM. The second identified locus involves rs2234962, a non-synonymous SNP (c.T757C, p. C151R) located within the sequence of BAG3 on chromosome 10q26. To assess whether coding mutations of BAG3 might cause monogenic forms of the disease, we sequenced BAG3 exons in 168 independent index cases diagnosed with familial DCM and identified four truncating and two missense mutations. Each mutation was heterozygous, present in all genotyped relatives affected by the disease and absent in a control group of 347 healthy individuals, strongly suggesting that these mutations are causing the disease.

CONCLUSION

This GWAS identified two loci involved in sporadic DCM, one of them probably implicates BAG3. Our results show that rare mutations in BAG3 contribute to monogenic forms of the disease, while common variant(s) in the same gene are implicated in sporadic DCM.

Two new cases of the Christchurch (Ch1) chromosome 21: evidence for clinical consequences of de novo deletion 21P-

We performed an investigation of two unrelated cases with extremal variants of chromosome 21 without visible materials of the short arms (Christchurch or Ch1 chromosome). In the first case chromosome 21p- was initially detected during routine cytogenetic amniocentesis. Chromosomal variant was inherited from phenotypically normal father to phenotypically normal fetus (phenotypically normal boy after the birth). The second case of chromosome 21p- was detected in 7 years old boy, referred to cytogenetic analysis due to mental retardation and mild congenital malformation, including prenatal hypoplasia, microcephaly, low-set dysplastic ears, short nose, micrognatia, short neck. Molecular characterization of 21p-variant chromosomes was performed by the use of FISH with DNA probes specific to the short arm and centromeric region of chromosome 21 (telomeric, beta-satellite, ribosomal, classical satellite and alphoid DNA probes). Chromosomes 21p-hybridized positively only with telomeric DNA at both chromosomal ends and alphoid DNA probes at centromeric region of the first patient. In second case (de novo deletion of 21p), the Ch1 was associated with clinical phenotype and loss of telomeric and subtelomeric DNA in the p-arm of chromosome 21. Therefore, the complete absent of the short arm of chromosome 21 may be considered as abnormal. We propose that de novo deletion 21p- could have negative consequences due to absence of large portion of chromosomal DNA from the p-arm (telomeric, satellite or ribosomal DNAs) and following imbalance in organization and functioning of genome.

MethDB--a public database for DNA methylation data

Methylation of cytosine in the 5 position of the pyrimidine ring is a major modification of the DNA in most organisms. In eukaryotes, the distribution and number of 5-methylcytosines (5mC) along the DNA is heritable but can also change with the developmental state of the cell and as a response to modifications of the environment. While DNA methylation probably has a number of functions, scientific interest has recently focused on the gene silencing effect methylation can have in eukaryotic cells. In particular, the discovery of changes in the methylation level during cancer development has increased the interest in this field. In the past, a vast amount of data has been generated with different levels of resolution ranging from 5mC content of total DNA to the methylation status of single nucleotides. We present here a database for DNA methylation data that attempts to unify these results in a common resource. The database is accessible via WWW (http://www.methdb.de). It stores information about the origin of the investigated sample and the experimental procedure, and contains the DNA methylation data. Query masks allow for searching for 5mC content, species, tissue, gene, sex, phenotype, sequence ID and DNA type. The output lists all available information including the relative gene expression level. DNA methylation patterns and methylation profiles are shown both as a graphical representation and as G/A/T/C/5mC-sequences or tables with sequence positions and methylation levels, respectively.

Structure and function of alleles in the 3' end region of human apoB gene

OBJECTIVE

To study the structure of alleles in the 3' end of the apoB gene in Han, Mongolian and Tibetan populations in China as well as the roles in the regulation of gene expression.

METHODS

DNA were obtained from human leukocytes by phenol-chloroform extraction and ethanol precipitation. PCR were carried out in a 50 microliters volume containing 50 ng genomic DNA as template. The Ssp1-digested products were loaded on a gradient acrylamide gel and run for 3 hours. The constructs containing alleles were tested in cultured HepG2 and HeLa cells using transient assays.

RESULTS

Sixteen alleles with different repeat number were characterized. All of the alleles varying from HVE22 to HVE52, allele HVE34 was the most common (58.4%), followed by allele HVE36 (13.8%) and HVE32 (10.5%). 258 PCR products were digested with Ssp1 and run in 4-12% PAGE. We detected the fragments of 266bp, 91 bp, 61 bp and 39 bp in almost all samples. The small alleles (including HVE22, HVE24, HVE26 and HVE36) decreased the expressive activity of the luciferase reporter, in contrary, the large alleles (including HVE44, HVE46 and HVE48) elevated obviously the expressive activity of the luciferase reporter.

CONCLUSIONS

More alleles with different number of tandem repeats in 3' end of apoB gene exist in the Chinese populations. The alleles in 3' end minisatellite of human apoB gene could control the expression of the gene itself.

Analysis of alphoid DNA variation and kinetochore size in human chromosome 21: evidence against pathological significance of alphoid satellite DNA diminutions

Centromeric alpha satellite DNA sequences are linked to the kinetochore CENP-B proteins and therefore may be involved in the centromeric function. The high heterogeneity of size of the alphoid blocks raises the question of whether small amount of alphoid DNA or "deletion" of this block may have a pathological significance in the human centromere. In the present study, we analysed the correlation between size variations of alphoid DNA and kinetochore sizes in human chromosome 21 by molecular cytogenetic and immunochemical techniques. FISH analyses of alpha satellite DNA sizes in chromosome 21 homologues correlated well with the variation of their physical size as determined by pulsed field gel electrophoresis (PFGE). By contrast, the immunostaining study of the same homologous chromosomes with antikinetochore antibodies suggested that there is no positive correlation between the alpha satellite DNA block and kinetochore sizes. FISH analysis of chromosome 21-specific alphoid DNA and immunostaining of kinetochore extended interphase chromatin fibers indicate that centromeric kinetochore-specific proteins bind to restricted areas of centromeric DNA arrays. Thus, probably, restricted regions of centromeric DNA play an important role in kinetochore formation, centromeric function and abnormal chromosome segregation leading to non-disjunction.

[Study of alpha-satellite DNA in cosmid libraries, specific for chromosomes 13, 21, and 22, using fluorescence in situ hybridization]

Fluorescent in situ hybridization (FISH) was employed in mapping the alpha-satellite DNA that was revealed in the cosmid libraries specific for human chromosomes 13, 21, and 22. In total, 131 clones were revealed. They contained various elements of centromeric alphoid DNA sequences of acrocentric chromosomes, including those located close to SINEs, LINEs, and classical satellite sequences. The heterochromatin of acrocentric chromosomes was shown to contain two different groups of alphoid sequences: (1) those immediately adjacent to the centromeric regions (alpha 13-1, alpha 21-1, and alpha 22-1 loci) and (2) those located in the short arm of acrocentric chromosomes (alpha 13-2, alpha 21-2, and alpha 22-2 loci). Alphoid DNA sequences from the alpha 13-2, alpha 21-2, and alpha 22-2 loci are apparently not involved in the formation of centromeres and are absent from mitotically stable marker chromosomes with a deleted short arm. Robertsonian translocations t(13q; 21q) and t(14q; 22q), and chromosome 21p-. The heterochromatic regions of chromosomes 13, 21, and 22 were also shown to contain relatively chromosome-specific repetitive sequences of various alphoid DNA families, whose numerous copies occur in other chromosomes. Pools of centromeric alphoid cosmids can be of use in further studies of the structural and functional properties of heterochromatic DNA and the identification of centromeric sequences. Moreover, these clones can be employed in high-resolution mapping and in sequencing the heterochromatic regions of the human genome. The detailed FISH analysis of numerous alphoid cosmid clones allowed the identification of several new, highly specific DNA probes of molecular cytogenetic studies--in particular, the interphase and metaphase analyses of chromosomes 2, 9, 11, 14, 15, 16, 18, 20, 21-13, 22-14, and X.

A compositional map of the cen-q21 region of human chromosome 21

A compositional map of the centromere and of the subcentromeric region of the long arm of human chromosome 21 was established by determining the GC levels (GC is the molar fraction of guanine+cytosine in DNA) of 11 YACs (yeast artificial chromosomes) covering this 13-14 Mb region which extends from the alpha-satellite sequences of the C(entromeric) band q11.1, through R(everse) band q11.2, to the proximal part of G(iemsa) band q21. The entire region is made up of GC-poor, or L, isochores with only one GC-rich H1 isochore, at least 2 Mb in size, located in band q21. The almost identical GC levels of the centromeric alpha-satellite repeats (38.5%), of R band q11.2 (39%), and of G bands (38-40%) provide a direct demonstration that base composition cannot be the only cause of the cytogenetic differences between C, G, and the majority of R bands, namely the H3- R bands (which do not contain the GC-richest H3 isochores). The results obtained also show that isochores may be as long as 6 Mb, at least in the GC-poor regions of the genome, and support previous observations suggesting that YACs from isochore borders are unstable and/or difficult to clone. Genes and CpG islands are very rare in the GC-poor region investigated, as expected from the fact that their concentration is proportional to the GC levels of the isochores in which they are contained.

High resolution multicolor fluorescence in situ hybridization using cyanine and fluorescein dyes: rapid chromosome identification by directly fluorescently labeled alphoid DNA probes

We tested DNA probes directly labeled by fluorescently labeled nucleotides (Cy3-dCTP, Cy5-dCTP, FluorX-dCTP) for high resolution uni- and multicolor detection of human chromosomes and analysis of centromeric DNA organization by in situ hybridization. Alpha-satellite DNA probes specific to chromosomes 1, 2, 3, 4 + 9, 5 + 19, 6, 7, 8, 10, 11, 13 + 21, 14 + 22, 15, 16, 17, 18, 20, 22, X and Y were suitable for the accurate identification of human chromosomes in metaphase and interphase cells. Cy3-labeled probes had several advantages: (1) a high level of fluorescence (5-10 times more compared with fluorescein-labeled probes); (2) a low level of fluorescence in solution, allowing the detection of target chromosomes in situ during hybridization without the washing of slides; and (3) high resistance to photobleaching during prolonged (1-2 h) exposure to strong light, thus allowing the use of a high energy mercury lamp or a long integration time during image acquisition in digital imaging microscopy for the determination of weak signals. For di- and multicolor fluorescence in situ hybridization (FISH), we successfully used different combinations of directly fluorophorated probes with preservation of images by conventional microscopy or by digital imaging microscopy. FluorX and Cy3 dyes allowed the use of cosmid probes for mapping in a one-step hybridization experiment. Cyanine-labeled fluorophorated DNA probes offer additional possibilities for rapid chromosome detection during a simple 15-min FISH procedure, and can be recommended for basic research and clinical studies, utilizing FISH.

Structural analysis of the minisatellite present at the 3' end of the human apolipoprotein B gene: new definition of the alleles and evolutionary implications

The internal structure of different alleles of the minisatellite present at the 3' end of the apolipoprotein B (ApoB) gene has been analysed by different approaches including sequencing. The repeat unit arrangements of the minisatellite on 570 chromosomes belonging to European and African populations were thus determined. It was possible to group the alleles using this structural criterion much more clearly than by the number of repeat units which can in some cases be misleading in case-control genetic epidemiological studies using such DNA sequences as markers. We were thus able to define five types (a to e) of alleles and their subtypes and to recognize clearly those which are, respectively, specific of the African and Caucasian populations. A phylogeny of the different alleles found in all human populations could also be deduced by this approach. The different putative mutational events leading from one type, or subtype, to the other were simply determined as point mutations, expansion/contraction and conversion events. Sequencing of one chimpanzee's allele suggested that the ApoB minisatellite was present before divergence between great apes and humans. It was determined also that a particular ApoB gene haplotype was in linkage disequilibrium with the minisatellite (a) type of alleles. This and the observation that the potential scaffold attachment regions (SAR) and topoisomerase II binding sites present in this minisatellite have a different distribution between the Caucasian and the African specific alleles suggest that the minisatellite could be involved in the epidemiology of coronary diseases.

Analysis of pericentromeric chromosome 21 specific YAC clones by FISH: identification of new markers for molecular-cytogenetic application

Fluorescence in situ hybridization (FISH) of chromosome 21 specific yeast artificial chromosome (YAC) clones after Alu-PCR (polymerase chain reaction) amplification has been used to find new region-specific DNA probes for the heterochromatic region of chromosome 21. Six overlapping YAC clones from a pericentromeric contig map (region 21cen-21q11) were analyzed. Four YAC clones were characterized as hybridizing to several chromosomal locations. They are, therefore, either chimeric or shared by different chromosomes. Two of them containing alphoid satellite DNA, are localized at the centromeric regions of chromosomes 13 and 21 (clone 243A11), and on 13cen, 21cen and 1q3 (clone 781G5); the two others are localized at both 21q11 and 13q2 (clone 759D3), and at 18p (clone 770B3). Two YACs were strongly specific for chromosome 21q11 only (clones 124A7 and 881D2). These YACs were used effectively as probes for identifications of chromosome 21 during metaphase and interphase analysis of 12 individuals, including three families with Down syndrome offspring, and 6 aminocyte samples. The location of YAC clones on 21q11 close to the centromeric region allows the application of these clones as molecular probes for the analysis of marker chromosomes with partial deletions of the long arm as well as for pre- and postnatal diagnosis of trisomy 21 when alphoid or more distal region-specific DNA probes are uninformative. Overlapping YAC clones covering human chromosome 21q may be systematically used to detect a set of band-specific DNA probes for molecular-cytogenetic application.

Prenatal diagnosis of trisomy 21 using interphase fluorescence in situ hybridization of post-replicated cells with site-specific cosmid and cosmid contig probes

Interphase fluorescence in situ hybridization (FISH) with chromosome 21-specific cosmid clones was used to identify trisomy 21 in cultured and uncultured amniotic cells. Two novel site-specific cosmid clones (regions 21q22 and 21qtel) were compared with a cosmid contig (Zheng et al., 1992). Correct identification of chromosome 21 copy number was made in 65-75 per cent of trisomic cells and in 70-75 per cent of normal disomic cells by using all the tested probes. However, the chromosome 21-specific telomeric probe (cos 17F8) showed the best results due to more intense and clearly visible hybridization. Utilization of a directly fluorophorated telomeric probe using Cy3-dCTP and FluorX-dCTP allows accurate detection of chromosome 21 in a fast 'one-step' FISH procedure on uncultured interphase nuclei. In addition, we compared the efficacy of FISH analysis for the total population of interphase cells and cells in the post-replication (late S, G2) periods of the cell cycle. Selective scoring of cells in the post-replicative period (showing a pair of hybridization signals on each chromatid of the replicated interphase chromosome) increased the number of informative nuclei by up to 95-97 per cent. This approach allows cells with overlapping chromosomes, artificial double hybridization signals on separate chromatids in interphase chromosomes, background hybridization, and polyploid cells to be analysed. Application of directly labelled telomeric cosmid probes and integral analysis of hybridized nuclei in the pre- and post-replication periods of the cell cycle may help to further improve the prenatal detection of trisomy 21.

Polymorphism at VNTR locus 3 to the apolipoprotein B gene in a Tunisian population: difference from other ethnic groups

The Hypervariable region (HVR) detected at the 3' end of the apolipoprotein B (Apo B) locus has been the subject of numerous studies. As for many VNTR (variable number of tandem repeat), this locus is highly polymorphic and until now about 20 alleles have been described. The genotype distribution in all populations follows the Hardy-Weinberg predictions. A bimodal pattern of allele frequency distribution is apparent in all Caucasoid populations. We have analyzed the frequencies of different alleles in a Tunisian population (123 individuals) by the polymerase chain reaction technique and compared our results to those obtained in several ethnic groups. It appears that the distributions of the allele frequencies are very different: for Caucasoid populations, there are two peaks of frequencies for alleles with 36 and 48 repeats, but alleles of intermediate lengths are more frequent. Hixson et al. [(1993) Hum Genet 91:475-479] have shown a similar difference between black and white American populations. We found the same results in a black African group. Some of the repeat units of this HVR contain a Ssp I restriction site and digestion of the PCR products by this enzyme gives different patterns on gradient acrylamide gel [Desmarais et al., 1993, Nucleic Acids Res 21:2179-2184.] The DNA of African individuals (42) has been analyzed to discover the origin of this new allele. Preliminary results indicate that these particular alleles probably arose by introgression from the African population into the Tunisian one.

Variant mapping of the Apo(B) AT rich minisatellite. Dependence on nucleotide sequence of the copy number variations. Instability of the non-canonical alleles

Because of its variations in length, the AT rich Hyper-Variable Region (HVR) of the 3' end of the Apolipoprotein B gene is used as a polymorphic maker in genetic studies. It contains a SspI site in its repeated motif and we used this feature to precisely analyse the internal structure of the different alleles found at this locus in a Caucasian population. We performed total digestion on 194 alleles as well as Minisatellite Variant Repeat mapping (MVR mapping: partial digestion) on 54. The results show that the level of length variability (in copy number) of the 5' end of this locus is at least two times higher than that of the 3' end. This could be correlated with the difference in nucleotide sequence between the two parts of the HVR and suggests the dependence on the primary structure of the mechanism that produces length variability. A molecular model is proposed to explain this result. Moreover, the sharp analysis of the minisatellite structure by the distribution of SspI sites reveals differences between long and short alleles, indicating that in most cases, no recombination occurs between alleles of different sizes. Finally the rare alleles exhibit a non-canonical structure. These important points could explain the bimodal distribution of the frequencies of the alleles in the population.

The polymorphism ApoB/4311 in patients with myocardial infarction and controls: the ECTIM Study

The polymorphism affecting codon 4311 of the apolipoprotein B gene (ApoB/4311) was investigated in a large case-control study in two French and one Northern Irish geographically defined populations. Cases were recruited 3 to 9 months after a myocardial infarction (MI) and controls were randomly selected from the population. The polymorphism was assessed using allele-specific oligonucleotides (ASO). The genotype frequencies of the ApoB/4311 polymorphism did not differ in Northern Ireland and France and were in Hardy-Weinberg equilibrium in all groups; strong associations with three other polymorphisms of the ApoB gene (XbaI, EcoRI, VNTR(34 repeats)) were observed and it was possible to identify highly sensitive and specific markers of the ApoB/4311 rare variant. Homozygotes for the ApoB 4311 rare variant were slightly less frequent in cases than in controls: 22 (4.4%) and 35 (6.7%) respectively (population adjusted chi 2 = 3.3 P less than 0.07), especially in Belfast: 6 (3.1%) and 12 (7.6%), respectively (P less than 0.06). Several lipid and lipoprotein parameters were measured. Consistently among control groups, rare homozygotes had lower mean levels of ApoB (P less than 0.02), triglycerides (P less than 0.02), and lipoprotein particles containing ApoE and ApoB (LpE:B; P less than 0.001) and a higher mean level of lipoprotein particles containing ApoAI and not ApoAII (LpAI; P less than 0.02) than heterozygotes and frequent homozygotes combined. The strong association between the ApoB/4311 polymorphism and LpE:B was also observed in patients with MI. When present in the homozygous form, the ApoB/4311 Asn----Ser variant is associated with a lipoprotein profile that is apparently favourable.

Analysis of mating systems in the schistosome-vector hermaphrodite snail Bulinus globosus by DNA fingerprinting

Bulinus globosus, one of the intermediate hosts for Schistosoma, is a hermaphrodite freshwater snail. Multilocus DNA fingerprinting was applied in order to investigate the mating system of this facultatively self-fertilizing species. By analysing DNA fingerprints of eight broods, we have shown that selfed and outcrossed individuals could be unambiguously distinguished by comparison with their parent fingerprints. First, selfed offspring patterns shared a higher number of bands with their mother than did outcrossed ones. Secondly, at least three paternal bands could be detected per outcrossed offspring pattern.

A new 5' sequence associated with mouse L1 elements is representative of a major class of L1 termini

Full-length L1 elements have been shown to possess, at their 5' end, tandem repeats called "A" or "F" types. By sequencing the 5' region of two large L1 copies that did not hybridize to A or F probes, we have identified a new sequence that is found at the 5' end of many L1 elements and that we call "V." The element characterized has no 200-bp tandem repetitive structure, and the new 5' sequence is not similar to the A or F sequences. The study of the relationships between the V and L1 sequences has shown that only half of the V (i.e., V-specific 5') sequences in the genome are linked to the 5' end of L1 copies. In related rodent species, a comparative study by Southern blot and PCR analysis of the V sequence suggests that this L1 subfamily has an ancient origin and that V sequence isolated from the remainder of the L1 element has been amplified during the evolution of the mouse genome.

Characterization of a Trypanosoma cruzi specific nuclear repeated sequence

We report the isolation of three different clones from a Trypanosoma cruzi genomic library bearing a common repeated sequence. This sequence is not tandemly repeated, and is dispersed on many chromosomes. All of the T. cruzi strains tested share this element. On the other hand, it is absent from the genome of other Kinetoplastida. The size of this element is about 10-12 kb, and its copy number is 220 in the T. cruzi Dm 28c genome. A transcript homologous to this sequence is detected in epimastigote forms of the parasite.

Pulsed-field gel electrophoresis determination of the genome size of obligate intracellular bacteria belonging to the genera Chlamydia, Rickettsiella, and Porochlamydia

The chromosome length of obligate intracellular procaryotes was determined by pulsed-field gel electrophoresis of intact or NotI- and SfiI-restricted genomes. Sizes averaged 2,100, 1,720, 1,550, 2,650, and 1,450 kilobases for Rickettsiella grylli, Rickettsiella melolonthae, Porochlamydia buthi, Porochlamydia chironomi, and Chlamydia psittaci and Chlamydia trachomatis, respectively. An SfiI restriction map of the R. melolonthae genome was derived.

DNA polymorphism in strains of the genus Brucella

Preparations of DNA from 23 Brucella strains including 19 reference strains were compared by restriction endonuclease analysis. Pulsed-field gel electrophoresis resulted in optimal resolution of fragments generated by digestion with low-cleavage-frequency restriction enzymes such as XbaI. By this technique, five electrophoretypes were distinguished in five reference strains of the different species, i.e., B. abortus, B. melitensis, B. suis, B. canis, and B. ovis. Minor profile differences allowed us to discriminate between most biovars within a species. However, the differences in the DNA patterns of different field strains of biovar 2 of B. melitensis were not sufficient to serve as markers for epidemiological studies. From the XbaI fragments, we were able to estimate the size of the genomes of B. abortus 544T and B. melitensis 16 MT. This method revealed a relationship between DNA fingerprints, species, and pathovars which could shed light on problems concerning the classification and evolution of members of the genus Brucella.

Comparative study of the L1 family in the genus Mus. Possible role of retroposition and conversion events in its concerted evolution

The long interspersed repetitive family L1 was analysed in different species belonging to the genus Mus. It is shown to be highly conserved even in M.n. setulosus, which diverged from the other species around ten million years ago. The study of the linkage between diagnostic restriction sites in the various species and the sequence variations of different regions of the L1Md repeat shows that the L1 family undergoes concerted changes involving subsets of repeats. The rate at which this homogenization process occurs does not appear to be the same for all the subfamilies detected. The L1Md repeat in the twelfth intron of the serum albumin gene of Balb/c mice is shown to be a recent insertion. The role retroposon- and gene conversion-like events may play in the concerted evolution of the L1 family is discussed.

Tissue specificity and organisation of CpG methylation in calf satellite DNA I

Examination of bovine satellite DNA I methylation within CpG dinucleotides has been made by restriction analysis. It is shown that variations in the methylation patterns occur between different tissues (brain, liver, thymus and sperm) . Some of the 8 Hpa II sites present per repeat are clearly undermethylated in sperm as compared to other tissues. Methylation is considered therefore, as a highly specific event. It is also shown that there is a spatial specificity in the methylation pattern of the 3 Hha I sites in all tissues. These results are discussed in the light of methylation and satellite DNA functions.

The organisation of the long range periodicity calf satellite DNA I variants as revealed by restriction enzyme analysis

The analysis of a large number of restriction sites within the long range periodicity calf satellite DNA I does not reveal a superimposable shorter repeat. Although some restriction sites are present in almost all the 100,000 tandemly arranged copies of the 1460 bp repetition unit, other sites such as Atu CI occur at much lower frequencies. When present they are distributed randomly along the satellite DNA molecules. The missing sites appear to result from random and presumably single base alterations. Digestion with the enzymes Hha I and Kpn I showed another type of variant to exist within the calf satellite DNA I. Unlike Atu CI the distributions of the variants detected by these enzymes are not random and organised on long stretches of satellite DNA. The possible functional significance and evolutionary implication of these results are discussed.

A method for detecting the coding DNA for a protein of known sequence in a collection of chimeric plasmids constructed with cDNAs

A rapid screening method for recognising plasmids containing copies of cDNA corresponding to proteins of known amino acid sequences, is described. The method is based on the computer prediction of the possible restriction sites in the cloned DNAs. It was tested on a series of proteins with known coding DNA sequences and a series of plasmid cloned cDNAs made from pure chicken globin mRNA.

A new site-specific endonuclease showing phenotypical crypticity in a tumorigenic strain of Agrobacterium tumefaciens

AtuBVI, an endonuclease showing new site-specificity, has been isolated from the tumorigenic strain IIBV7 of Agrobacterium tumefaciens, and is undetectable in the non-tumorigenic sister strain IIBNV6. AtuBVI degrades IIBV7 DNA in vitro and should, therefore, be regarded as being phenotypically cryptic in the bacterial cell; it also shows anomalous behavior under cerain incubation conditions. These properties point to a possible role for this enzyme in the insertion of exogenous Ti-plasmid DNA into plant tissues during tumorigenesis.

A possible structure for calf satellite DNA I

Calf satellite DNA I (p = 1.715) has been hydrolysed by a number or restriction endonucleases. It consists of a repeating unit of 1460 nucleotide pairs within which the sites of Eco R II Mbo I, Sac I, Alu I, Ava II and Hha I were localised in comparison with those of Eco R I and Hind II. The distribution of the Hpa II, Sac I, Hha I, Hinf I and Mbo II sites within calf satellite DNA I, as well as that of several restriction endonuclease sites within calf satellite DNA III (p = 1.705) allowed me to define subsatellite fractions. Furthermore, some of the sites of the CpG containing restriction enzymes Hpa II and Hha I are lacking. The possible implications of these results are discussed.