Instability of short-sequence DNA repeats of pear pathogenic Erwinia strains from Japan and Erwinia amylovora fruit tree and raspberry strains

An array of short-sequence DNA repeats (SSRs) occurs in the plasmid pEA29 of the fire blight pathogen Erwinia amylovora. A large number of "fruit tree" strains, mainly from Central and Western Europe, were screened for their SSR numbers, and the analyses were extended to five raspberry strains from North America and six pear pathogenic Erwinia strains from Japan. The repeat ATTACAGA present in all E. amylovorastrains was found to be reiterated 3 to 15 times. The Japanese strains contained the major repeat sequence GGATTCTG, which was reiterated 16 to 24 times. ATTACAGG, which resembles the SSR of E. amylovora, was reiterated two or three times. In a novel approach, sequencing gels were used to visualize the rare occurrence of shorter arrays (down to three repeats) in E. amylovoraand the Japanese Erwinia strains. Changes in the repeat numbers in E. amylovora were observed repeatedly when the bacteria had been exposed to stress conditions. The repeat structures of homo- and heteroduplices of PCR-amplified repeats were also analyzed by cleavage of annealed molecules with the single-strand-specific endonuclease from bacteriophage T4. Not only heteroduplexes, but also homoduplexes showed non-matching regions in the SSRs, which could arise from transient formation of loops due to strand slippage during the assays.

Genetic polymorphisms in the renin-angiotensin-aldosterone system associated with expression of left ventricular hypertrophy in hypertrophic cardiomyopathy: a study of five polymorphic genes in a family with a disease causing mutation in the myosin binding protein C gene

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is an inherited disease of the sarcomere characterised clinically by myocardial hypertrophy and its consequences. Phenotypic expression is heterogeneous even within families with the same aetiological mutation and may be influenced by additional genetic factors.

OBJECTIVE

To determine the influence of genetic polymorphisms of the renin-angiotensin-aldosterone system (RAAS) on ECG and two dimensional echocardiographic left ventricular hypertrophy (LVH) in genetically identical patients with HCM.

PATIENTS AND METHODS

Polymorphisms of five RAAS components were determined in 26 gene carriers from a single family with HCM caused by a previously identified myosin binding protein C mutation. Genotypes associated with a higher activation status of the RAAS were labelled "pro-LVH genotypes".

RESULTS

There was a non-biased distribution of pro-LVH genotypes in the gene carriers. Those without pro-LVH genotypes did not manifest cardiac hypertrophy whereas gene carriers with pro-LVH genotypes did (mean (SD) left ventricular muscle mass 190 (48) v 320 (113), p = 0.002; interventricular septal thickness 11.5 (2.0) v 16.4 (6.7), p = 0.01; pathological ECG 0% (0 of 10) v 63% (10 of 16), respectively). Multivariate analysis controlling for age, sex, and hypertension confirmed an independent association between the presence of pro-LVH polymorphisms and left ventricular mass. When each polymorphism was assessed individually, carriers of each pro-LVH genotype had a significantly greater left ventricular mass than those with no pro-LVH mutation; these associations, with the exception of cardiac chymase A AA polymorphism (p = 0.06), remained significant in multivariate analysis.

CONCLUSION

Genetic polymorphisms of the RAAS influence penetrance and degree of LVH in 26 gene carriers from one family with HCM caused by a myosin binding protein C mutation.

Genomic structure and fine mapping of the two human filamin gene paralogues FLNB and FLNC and comparative analysis of the filamin gene family

The genomic structure of the filamin gene paralogues FLNB and FLNC was determined and related to FLNA. FLNB consists of 45 exons and 44 introns and spans approximately 80 kb of genomic DNA. FLNC is divided into 48 exons and 47 introns and covers approximately 29.5 kb of genomic DNA. A previously unknown intron was found in FLNA. The comparison of all three filamin gene paralogues revealed a highly conserved exon-intron structure with significant differences in the exons 32 of all paralogues encoding the hinge I region, as well as the insertion of a novel exon 40A in FLNC only. Gene organization does not correlate with the domain structures of the respective proteins. To improve candidate gene cloning approaches, FLNB was precisely mapped at 3p14 in an interval of 0.81 cM between WI3771 and WI6691 and FLNC at 7q32 in an interval of 2.07 cM between D7S530 and D7S649.

Apical hypertrophic cardiomyopathy due to a de novo mutation Arg719Trp of the beta-myosin heavy chain gene and cardiac arrest in childhood. A case report and family study

Hypertrophic cardiomyopathy (HCM) is a myocardial disease with variable phenotpye and genotype. To demonstrate that the mutation Arg719Trp in the cardiac beta-myosin heavy chain (beta MHC) gene is a high risk factor for sudden death and can be associated with an unusual apical non-obstructive HCM, we report the case of a 6 1/2 year old boy, who suffered cardiac arrest. The proband had a de novo mutation of the beta MHC gene (Arg719Trp) on the paternal beta MHC allele and a second maternally transmitted mutation (Met349Thr), as was shown previously (Jeschke et al. 1998 (11)). Here we report the clinical phenotype of the proband and of his relatives in detail. The proband had a marked apical and midventricular hypertrophy of the left and right ventricle without obstruction. There was an abnormal relaxation of both ventricles. Holter monitoring detected no arrhythmia. Ventricular fibrillation was inducible only by aggressive programmed stimulation. The boy died 3 1/2 years later after another cardiac arrest due to arrhythmia. Five carriers of the Met349Thr mutation in the family were asymptomatic and had no echocardiographic changes in the heart, suggesting a neutral inherited polymorphism or a recessive mutation. It is concluded that there is an association of the mutation Arg719Trp in the beta-myosin heavy chain with sudden cardiac death in a young child. Disease history in conjunction with the genetic analysis suggests that the implantation of a defibrillator converter would have been a beneficial and probably life saving measure.

A newly created splice donor site in exon 25 of the MyBP-C gene is responsible for inherited hypertrophic cardiomyopathy with incomplete disease penetrance

BACKGROUND

Hypertrophic cardiomyopathy is a myocardial disorder resulting from inherited sarcomeric dysfunction. We report a mutation in the myosin-binding protein-C (MyBP-C) gene, its clinical consequences in a large family, and myocardial tissue findings that may provide insight into the mechanism of disease.

METHODS AND RESULTS

History and clinical status (examination, ECG, and echocardiography) were assessed in 49 members of a multigeneration family. Linkage analysis implicated the MyBP-C gene on chromosome 11. Myocardial mRNA, genomic MyBP-C DNA, and the myocardial proteins of patients and healthy relatives were analyzed. A single guanine nucleotide insertion in exon 25 of the MyBP-C gene resulted in the loss of 40 bases in abnormally processed mRNA. A 30-kDa truncation at the C-terminus of the protein was predicted, but a polypeptide of the expected size ( approximately 95 kDa) was not detected by immunoblot testing. The disease phenotype in this family was characterized in detail: only 10 of 27 gene carriers fulfilled diagnostic criteria. Five carriers showed borderline hypertrophic cardiomyopathy, and 12 carriers were asymptomatic, with normal ECG and echocardiograms. The age of onset in symptomatic patients was late (29 to 68 years). In 2 patients, outflow obstruction required surgery. Two family members experienced premature sudden cardiac death, but survival at 50 years was 95%.

CONCLUSIONS

Penetrance of this mutation was incomplete and age-dependent. The large number of asymptomatic carriers and the good prognosis support the interpretation of benign disease.

[Genetic causes of hypertrophic cardiomyopathy]

Hypertrophic cardiomyopathy is a dominantly inherited disease of the heart. Heterogeneous sets of mutations responsible for this condition have been identified in seven genes coding for proteins involved in the contraction mechanism or in the control of contraction of the myocardium. Known mutations imply structural and functional changes in the following proteins: in ventricle specific beta-myosin heavy chain, in essential and regulatory myosin light chains, in troponin subunits T and I, in alpha-tropomyosin and in myosin binding protein-C. The gene of one additional genomic HCM-locus is not known. Since two thirds or more of all cases can be traced to one of the respective genes, HCM has been classified as a disease of the cardiac sarcomere. Heterogeneity does not only exist between genes, but also within genes. At least 84 different mutations have been identified to date. More than half of them have been detected in the beta-myosin heavy chain gene. Thus, mutations in this gene account for most of the cases of HCM. The extent of data about causes is in contrast to the lack of definite knowledge about pathogenic mechanisms. Since the disorder is in many cases mild with symptoms developing frequently not before the end of the second decade, myocardial dysfunctions can presumably not directly be traced to altered contractility, but rather to effects which accumulate with a long asymptomatic lag period and which gradually lead to hypertrophy, conduction problems and ultimately to cardiac failure. The disease may be considered as an indirect and secondary response to a mildly distorted contraction process. The rapid progress in the analysis of causes suggests that the study of genes will assume a role in the context of the clinical management of HCM, in particular regarding diagnosis, prognosis, counselling of patients and families and--possibly--therapy.

A high risk phenotype of hypertrophic cardiomyopathy associated with a compound genotype of two mutated beta-myosin heavy chain genes

Hypertrophic cardiomyopathy (HCM) is a genetically and clinically heterogeneous myocardial disease that is in most cases familial and transmitted in a dominant fashion. The most frequently affected gene codes for the cardiac (ventricular) beta-myosin heavy chain. We have investigated the genetic cause of an isolated case of HCM, which was marked by an extremely severe phenotype and a very early age of onset. HCM is normally not a disease of small children. The proband was a boy who had suffered cardiac arrest at the age of 6.5 years (resuscitation by cardioconversion). Upon screening of the beta-myosin heavy chain gene as a candidate, two missense mutations, one in exon 19 (Arg719Trp) and a second in exon 12 (Met349Thr), were identified. The Arg719Trp mutation was de novo, as it was not found in the parents. In contrast, the Met349Thr mutation was inherited through the maternal grandmother. Six family members were carriers of this mutation but only the proband was clinically affected. Segregation and molecular analysis allowed us to assign the Met349Thr mutation to the maternal and the Arg719Trp de novo mutation to the paternal beta-myosin allele. Thus, the patient has no normal myosin. We interpret these findings in terms of compound heterozygosity of a dominant (Arg719Trp) and a recessive (Met349Thr) mutation. Whereas a single mutated Arg719Trp allele would be sufficient to cause HCM, the concurrent Met349Thr mutation alone does not apparently induce the disease. Nevertheless, it conceivably contributes to the particularly severe phenotype.

Clinical features of hypertrophic cardiomyopathy caused by mutation of a "hot spot" in the alpha-tropomyosin gene

OBJECTIVES

We studied the clinical and genetic features of familial hypertrophic cardiomyopathy (FHC) caused by an Asp175Asn mutation in the alpha-tropomyosin gene in affected subjects from three unrelated families.

BACKGROUND

Correlation of genotype and phenotype has provided important information in FHC caused by beta-cardiac myosin and cardiac troponin T mutations. Comparable analyses of hypertrophic cardiomyopathy caused by alpha-tropomyosin mutations have been hampered by the rarity of these genetic defects.

METHODS

The haplotypes of three kindreds with FHC due to an alpha-tropomyosin gene mutation, Asp175Asn, were analyzed. The cardiac histopathologic findings of this mutation are reported. Distribution of left ventricular hypertrophy in affected members was assessed by two-dimensional echocardiography, and patient survival rates were compared.

RESULTS

Genetic studies defined unique haplotypes in the three families, demonstrating that independent mutations caused the disease in each. The Asp175Asn mutation caused cardiac histopathologic findings of myocyte hypertrophy, disarray and replacement fibrosis. The severity and distribution of left ventricular hypertrophy varied considerably in affected members from the three families (mean maximal wall thickness +/- SD: 24 +/- 4.5 mm in anterior septum of Family DT; 15 +/- 2.7 mm in anterior septum and free wall of Family DB; 18 +/- 2.1 mm in posterior septum of Family MI), but survival was comparable and favorable.

CONCLUSIONS

Nucleotide residue 579 in the alpha-tropomyosin gene may have increased susceptibility to mutation. On cardiac histopathologic study, defects in this sarcomere thin filament component are indistinguishable from other genetic etiologies of hypertrophic cardiomyopathy. The Asp175Asn mutation can elicit different morphologic responses, suggesting that the hypertrophic phenotype is modulated not by genetic etiologic factors alone. In contrast, prognosis reflected genotype; near normal life expectancy is found in hypertrophic cardiomyopathy caused by the alpha-tropomyosin mutation Asp175Asn.

Cardiac myosin binding protein-C gene splice acceptor site mutation is associated with familial hypertrophic cardiomyopathy

Familial hypertrophic cardiomyopathy (FHC) is an autosomal dominant disease characterized by a ventricular hypertrophy predominantly affecting the interventricular septum and associated with a large extent of myocardial and myofibrillar disarray. It is the most common cause of sudden death in the young. In the four disease loci found, three genes have been identified which code for beta-myosin heavy chain, cardiac troponin T and alpha-tropomyosin. Recently the human cardiac myosin binding protein-C (MyBP-C) gene was mapped to chromosome 11p11.2 (ref. 8), making this gene a good candidate for the fourth locus, CMH4 (ref. 5). Indeed, MyBP-C is a substantial component of the myofibrils that interacts with several proteins of the thick filament of the sarcomere. In two unrelated French families linked to CMH4, we found a mutation in a splice acceptor site of the MyBP-C gene, which causes the skipping of the associated exon and could produce truncated cardiac MyBP-Cs. Mutations in the cardiac MyBP-C gene likely cause chromosome 11-linked hypertrophic cardiomyopathy, further supporting the hypothesis that hypertrophic cardiomyopathy results from mutations in genes encoding contractile proteins.

Identification of gene defects by linkage analysis: use in inherited cardiomyopathies

One of the central activities of current medical (including cardiological) research is identification of the causes of inherited diseases. The goals are the determination of genes and risk factors, introduction of new diagnostic standards and ultimately refinement of therapies. In cardiac disorders, molecular causes have been detected for certain types of hypertrophic cardiomyopathy (HCM), a disease characterized by increased ventricular wall thickness, a high risk of arrhythmias and an increased frequency of sudden cardiac death. The first known cause of HCM was a point mutation in the cardiac beta-myosin heavy chain gene on chromosome 14, detected using a genetic mapping procedure based on linkage of the clinical phenotype with genomic marker sequences. Additional missense mutations have been located in the globular head of beta-myosin, and other disease loci have been identified on chromosomes 1, 11, and 15; the disease genes in these loci have not yet been determined, however.

Identification of a mutation near a functional site of the beta cardiac myosin heavy chain gene in a family with hypertrophic cardiomyopathy

Several mutations within the gene coding for the cardiac beta myosin heavy chain (designed MYH7) have been shown to be responsible for Familial Hypertrophic Cardiomyopathy (FHC) in several families, and evidence of genetic heterogeneity has been reported. To investigate the MYH7 gene as the cause of the disease in a small family with FHC, inheritance of the disease and chromosome 14 q11-q12 markers haplotype were studied, exons coding for the head domain of the cardiac beta myosin heavy chain (beta MHC) were analysed for mutations by MDE gel electrophoresis, and sequenced. We report a mutation within exon eight of the MYH7 gene at a very conserved amino acid at position 232, which results in the conversion of an asparagine to serine. This residue Asn-232 is located in a MHC area that has been recently identified as a critical site for ATPase activity. According to recent results on the three-dimensional structure of the myosin head or subfragment-1 (S1), Asn-232 is located in an alpha-helix which forms part of the nucleotide binding pocket. Although this mutation affects an active site, it seems to be associated with a favourable prognosis and a weak penetrance in this family.

Alpha-tropomyosin and cardiac troponin T mutations cause familial hypertrophic cardiomyopathy: a disease of the sarcomere

We demonstrate that missense mutations (Asp175Asn; Glu180Gly) in the alpha-tropomyosin gene cause familial hypertrophic cardiomyopathy (FHC) linked to chromosome 15q2. These findings implicated components of the troponin complex as candidate genes at other FHC loci, particularly cardiac troponin T, which was mapped in this study to chromosome 1q. Missense mutations (Ile79Asn; Arg92Gln) and a mutation in the splice donor sequence of intron 15 of the cardiac troponin T gene are also shown to cause FHC. Because alpha-tropomyosin and cardiac troponin T as well as beta myosin heavy chain mutations cause the same phenotype, we conclude that FHC is a disease of the sarcomere. Further, because the splice site mutation is predicted to function as a null allele, we suggest that abnormal stoichiometry of sarcomeric proteins can cause cardiac hypertrophy.

Myosin mutations in hypertrophic cardiomyopathy and functional implications

Hypertrophic cardiomyopathy (HCM) can be an inherited disorder. Typically, the inheritance is dominant and genetic cases account for about 50% of all patients with this pathology. Four different HCM loci have been mapped to different chromosomes (no. 1, 11, 14 and 15), yet, only one responsible gene has been identified. It is the beta myosin heavy chain gene on chromosome 14, which is expressed in ventricles and in slow skeletal muscle fibers. A large number of missense mutations has been reported which are predominantly located in the globular head region of the beta myosin. An apparent hot spot of mutation has been detected within exon 13 of the gene, corresponding to amino acid position 403. Although the functional consequences of the various mutations for the activity of beta myosin are not known, by inference and on the basis of published data, it may be suggested that a mutation in position 403 affects the myosin-actin dissociation in the contractile cycle. Despite our knowledge of mutations in the myosin gene, and of many of the pathological sequelas, there still is insufficient information which precludes unequivocal conclusions on the molecular mechanisms by which the pathogenesis of the myosin deficient heart develops. Molecular biology and genetics should help to define the determinants of this disease.

Mapping of the actomyosin interfaces

Recombinant DNA methods were used to obtain soluble, undenatured fragments of the heavy chain of myosin subfragment 1 (S-1). These fragments were of preselected lengths and could include protease-sensitive segments that are destroyed when other preparation methods are used. Actin binding by each of the three contiguous segments (residues 1-248, 249-524, and 518-722, essentially spanning the entire S-1 heavy chain) was demonstrated. ATP binding, comparable to that of native S-1, was obtained only with a segment consisting of residues 1-524. Competition among the various fragments for actin was also studied. The data are discussed in relation to the recently reported resolved structure of S-1 [Rayment, I., Rypnieski, R. W., Schmidt-Bäse, K., Smith, R., Tomchick, D. R., Benning, M. M., Winkelmann, D. A., Wesenberg, G. & Holden, H. M. (1993) Science 261, 50-58].

[Research in gene therapy--its status in Germany]

Progress in mammalian molecular biology and in the analysis of the human genome has allowed to identify the causes of an increasing number of human diseases in recent years. Newly developed gene transfer techniques were reason to implement new therapeutic concepts. By means of viral vectors or other transfer vehicles genes can be introduced into cells of the human body in order to replace a deficient function (in inherited diseases) or to play a role in defending the body (against cancer or, in the cardiovascular field, eventually by preventing restenosis). Despite considerable achievements of current DNA transfer technologies it seems premature to qualify gene therapy already as a new medical practice. The development in Germany is characterized by a late start in this field of research. The number of projects is correspondingly small. However, it may be expected that newly initiated governmental support of gene therapy research will lead to an expansion of the activities in this area.

Exclusion of cardiac myosin heavy chain and actin gene involvement in hypertrophic cardiomyopathy of several French families

Familial hypertrophic cardiomyopathy (FHC) is characterized by idiopathic myocardial hypertrophy, which often and predominantly involves the interventricular septum. The disease is transmitted as an autosomal dominant trait, and its major risk is sudden death. It was recently demonstrated that this disease is genetically heterogeneous and that in 13 of 18 unrelated families the morbid locus, termed FHC-1, maps to chromosome 14q11-12 in and/or very near the cardiac beta-myosin heavy chain gene. We have performed linkage analysis with five chromosomal markers detecting polymorphisms in either the cardiac beta-myosin heavy chain gene or the cardiac actin gene (located on chromosome 15q) on eight families from different regions of France. We show that 1) it is possible to analyze medium-sized families by using highly informative microsatellite markers located in these genes and 2) the disease is not linked to the two contractile protein genes in any of these families. Moreover, 10-20% of chromosome 14 and 20-40% of chromosome 15 in the vicinity of the respective markers were excluded as possible locations for the morbid locus. These results provide new insights into the identification of the genes responsible for FHC.

The regulation of the human beta myosin heavy-chain gene

The human myosin heavy-chain (MHC) genes for cardiac and skeletal muscle exist as a multigene family with eight or more non-allelic genes. Two of them code for the cardiac alpha and beta myocin HCs. They are located on chromosome 14. The skeletal muscle myosin HC genes are on chromosome 17. The cardiac MHCs coexist in the heart, however, with a distinct distribution within cardiac tissue of the human adult. alpha-MHC is predominantly found in the atria and beta-MHC is found in the ventricles. Both genes are also expressed in certain types of skeletal muscle fibers. We have sequenced the beta-gene in its entire length and have further studied in detail its expression in muscle cells. Promoter activities were tested using DNA-mediated gene transfer in cultured chicken embryonic myoblasts. By deletion mapping of the 5' flanking region of the beta-gene a candidate signal sequence was identified in a region which stimulates the promoter in a tissue specific and differentiation dependent mode. The presumed signal was located about 210 bp 5' to the basic promoter which, by itself, is almost inactive, even in muscle cells. The sequence of the signal (CAGCTG) has homology to known E-box sequences. E-boxes (consensus sequence CANNTG) constitute a family of transcription control sites frequently found upstream of muscle genes. In nuclear extracts of cardiac and skeletal muscle (of rabbit) a protein was identified which binds to the region containing the E-box like motif of the beta-gene. Since this protein was present in both types of muscle, overlapping expression control patterns are assumed to operate in these tissues.

Analysis of a dystrophin gene deletion by amplification of mRNA isolated from DMD myotubes cultured in vitro

The most frequent causes for the X-linked muscular dystrophy of the allelic Duchenne (DMD) or Becker (BMD) type are partial deletions of the dystrophin gene. These mutations are accompanied either by disrupted or by preserved translational reading frames in mRNAs derived from the deleted genes. As a rule, the reading frame is destroyed in the more severe DMD, whereas it is preserved in the less severe BMD (M. Koenig et al., 1989, Am. J. Hum. Genet. 45, 498-506). We have analyzed in detail a deletion that was detected in a fetus at risk of DMD. The analysis of this mutation included the delineation of the altered subregion in the dystrophin mRNA. mRNA was isolated from myotubes derived from embryonic DMD myoblasts propagated in vitro. This study was based on enzymatic amplification by the polymerase chain reaction (PCR) of dystrophin mRNA and direct sequencing of the amplified cDNA. Exons 47 to 50 were found to be missing in the mRNA. The splicing of exon 46 to exon 51 resulted in a reading frameshift, indicating that this mutation is likely to be responsible for a DMD type of dystrophy. The clinical diagnosis of DMD for a 10-year-old patient in this family was compatible with the "reading frame" assumption.

The complete sequence of the human beta-myosin heavy chain gene and a comparative analysis of its product

We have isolated and sequenced the gene and the cDNA coding for the human cardiac beta-myosin heavy chain (designated MYH7). The gene is 22,883 bp long. The 1935 amino acids of this protein (Mr223,111) are encoded by 38 exons. The 5' untranslated region (86 bp) is split by two introns. The 3' untranslated region is 114 bp long. Three Alu repeats were identified within the gene and a fourth one in the 3' flanking intergenic region. The molecular organization of this gene reflects the conservative pattern with respect to size, coding ratio, and number or position of introns characteristic of vertebrate sarcomeric myosin heavy chain genes. The protein sequence of the human beta-heavy chain was compared with corresponding (homologous) sequences of rabbit, rat, and hamster as well as with the (heterologous) embryonic heavy chain sequences of rat, chicken, and man. The results show that protein subregions responsible for basic functions of myosin heavy chains (nucleotide binding and actin binding) are very similar in homologous and heterologous heavy chains. Regions that differ in their primary sequences in heterologous heavy chains appear to be highly conserved within mammalian beta-myosin heavy chains. Constant and variable subregions of heavy chains are discussed in terms of functional significance and evolutionary relatedness.

Expression of human beta-myosin heavy chain fragments in Escherichia coli; localization of actin interfaces on cardiac myosin

A cDNA clone coding for an internal fragment of slow-cardiac beta-myosin heavy chain was isolated from a lambda gt10 human skeletal muscle library. Six overlapping cDNA subclones, which span myosin heavy chain subregions and presumably interact with actin, were derived from this clone, fused to a beta-galactosidase vector and expressed in Escherichia coli. Three of the subclones were obtained by PCR (polymerase chain reaction) which enables gene or cDNA fragments to be amplified independently of preexisting restriction sites. Initially, various experiments were carried out using a long MHC (myosin heavy chain) fusion protein containing the 50 kDa-20 kDa connecting region, the whole 20 kDa region and the short subfragment 2 region. This MHC fusion protein was chemically or proteolytically cleaved in the same conditions as the native myosin molecule. Whole and truncated forms of the MHC fusion protein were separated on polyacrylamide gels, electroblotted on nitrocellulose sheets and renatured. They were then assayed in overlay experiments with F-actin and/or myosin light chains in solution. Specific antibodies were used to detect interactions between heavy chain fragments and F-actin or light chains. We thus observed that one long heavy chain fragment synthesized by E. coli behaved like proteolytic or chemical MHC preparations made from native myosin molecules. Two chymotryptic fragments of the MHC fusion protein, which are soluble at low ionic strength, cosedimented with F-actin in solution. Our results demonstrate that, in actin overlay experiments with whole fusion proteins, interactions seem to be due to the heavy chain fragment, not to the bacterial component. All interactions were non ATP-sensitive. We further investigated the possible participation of the six recombinant MHC fragments in contributing to the actomyosin interfaces on the 50 kDa-20 kDa regions of the human cardiac beta-MHC. The present procedure, which enables the synthesis of any MHC fragment independent of any protease site, is a powerful new tool for studying structure-function relationships within the myosin molecule family.

A molecular basis for familial hypertrophic cardiomyopathy: a beta cardiac myosin heavy chain gene missense mutation

A point mutation in exon 13 of the beta cardiac myosin heavy chain (MHC) gene is present in all individuals affected with familial hypertrophic cardiomyopathy (FHC) from a large kindred. This missense mutation converts a highly conserved arginine residue (Arg-403) to a glutamine. Affected individuals from an unrelated family lack this missense mutation, but instead have an alpha/beta cardiac MHC hybrid gene. Identification of two unique mutations within cardiac MHC genes in all individuals with FHC from two unrelated families demonstrates that defects in the cardiac MHC genes can cause this disease. The pathology resulting from a missense mutation at residue 403 further suggests that a critical function of myosin is disrupted by this mutation.

A molecular basis for familial hypertrophic cardiomyopathy: an alpha/beta cardiac myosin heavy chain hybrid gene

An alpha/beta cardiac myosin heavy chain (MHC) hybrid gene is coinherited with familial hypertrophic cardiomyopathy (FHC) in one kindred. FHC is a disease of the heart muscle characterized by a thickening of the left ventricular wall with myocyte and myofibrillar disarray that is inherited as an autosomal dominant trait. We demonstrate here and in the accompanying article that the cardiac MHC genes, which encode integral myofibrillar components, are mutated in all affected individuals from two unrelated families with FHC. In one kindred, an unequal crossover event during meiosis may have produced the alpha/beta cardiac MHC hybrid gene that is present in affected individuals. We conclude that mutations in the cardiac MHC genes can cause FHC.

Regulation of myosin heavy chain expression in the hearts of hypertensive rats by testosterone

Stroke-prone spontaneously hypertensive rats were used for our investigation of the influence of prepubertal gonadectomy and testosterone substitution on blood pressure, cardiac hypertrophy, and the expression of ventricular myosin heavy chain (MHC) isoenzymes at different developmental stages. Blood pressure and the degree of cardiac hypertrophy were decreased by castration and increased by testosterone substitution. We found the same relative distributions of MHC isoforms on the protein level (investigated by pyrophosphate electrophoresis) and on the messenger RNA level (investigated by the polymerase chain reaction). Castration favored the expression of the beta-MHC form, and testosterone substitution enhanced the expression of the alpha-MHC form. These effects were more pronounced in 8-week-old than in 14-16-week-old animals. We conclude that testosterone regulates cardiac MHC expression on a pretranslational level. This regulation is independent of hemodynamic load or cardiac hypertrophy.

The polymerase chain reaction: an improved method for the analysis of nucleic acids

The polymerase chain reaction (PCR) is a method for the selective amplification of DNA or RNA segments of up to 2 kilobase-pairs (kb) or more in length. Synthetic oligonucleotides flanking sequences of interest are used in repeated cycles of enzymatic primer extension in opposite and overlapping directions. The essential steps in each cycle are thermal denaturation of double-stranded target molecules, primer annealing to both strands and enzymatic synthesis of DNA. The use of the heat-stable DNA polymerase from the archebacterium Thermus aquaticus (Taq polymerase) makes the reaction amenable to automation. Since both strands of a given DNA segment are used as templates, the number of target sequences increases exponentially. The reaction is simple, fast and extremely sensitive. The DNA or RNA content of a single cell is sufficient to detect a specific sequence. This method greatly facilitates the diagnosis of mutations or sequence polymorphisms of various types in human genetics, and the detection of pathogenic components and conditions in the context of clinical research and diagnostics; it is also useful in simplifying complex analytical or synthetic protocols in basic molecular biology. This article describes the principles of the reaction and discusses the applications in different areas of biomedical research.

Isolation and characterization of the complete human beta-myosin heavy chain gene

The entire gene coding for the human beta-myosin heavy chain has been isolated from genomic EMBL3A phage libraries by chromosomal walking starting from clone gMHC-1, reported earlier (Appelhans and Vosberg 1983). gMHC-1 has been shown to carry coding information for the C-terminal two-thirds of beta-myosin heavy chain, which is expressed in cardiac muscle and in slow skeletal muscle fibers (Lichter et al. 1986). Three DNA clones were identified as overlapping with gMHC-1 by restriction mapping and DNA sequencing. They span a 30-kb region in the genome. About 22 kb extend from the initiation codon ATG to the poly(A) addition site. The clones include about 4 kb of 5' flanking sequences upstream of the promoter. Comparisons of beta- and alpha-myosin heavy chain sequences indicate that gene duplication of the cardiac myosin heavy chain isogenes preceded the mammalian species differentiation.

Direct sequencing of polymerase chain reaction amplified DNA fragments through the incorporation of deoxynucleoside alpha-thiotriphosphates

The direct sequencing of DNA generated by the polynucleotide chain reaction, via the incorporation of phosphorothioate nucleotides and followed by treatment with an alkylating reagent that cleaves specifically at the phosphorothioate positions, is described. The Taq polymerase used in the amplification reaction incorporates the Sp-diastereomer of the deoxynucleoside 5'-O-(1-thiotriphosphates) as efficiently as the natural nucleotides. Chemical degradation of the phosphorothioate-containing DNA fragment can be performed with either 2-iodoethanol or 2,3-epoxy-1-propanol. The higher reactivity of 2,3-epoxy-1-propanol allows less reagent to be used to obtain the same amount of degradation as with 2-iodoethanol.

Enzymatic amplification of myosin heavy-chain mRNA sequences in vitro

We have developed a procedure that detects the presence of mRNA coding for human beta-myosin heavy chain in small amounts of total, unfractionated RNA isolated from heart or skeletal muscle. The protocol is based on the enzymatic amplification in vitro of a selected 106-bp myosin isotype-specific subregion of this mRNA. The method, which is a modification of the so-called "polymerase chain reaction," requires two synthetic oligonucleotide primers (20-mers), reverse transcriptase, and DNA polymerase I (Klenow fragment). Two principle steps are involved: (i) the selected mRNA subregion is converted into a double-stranded cDNA, and (ii) this cDNA is amplified in 22 synthetic cycles. After gel electrophoresis and blotting the amplification product is identified by hybridization with a third oligonucleotide recognizing the region between the two primer annealing sites, and by restriction mapping. Only mRNA from muscle tissue promoted formation of the amplified 106-bp fragment. We estimate that less than 30,000 beta-myosin heavy-chain mRNA molecules are sufficient to produce a signal. The procedure is fast, specific, and very sensitive. It may be used in muscle gene expression studies with small numbers of cells or even in single muscle fibers.

Partial characterization of the human beta-myosin heavy-chain gene which is expressed in heart and skeletal muscle

A human myosin heavy-chain gene, cloned in gamma Charon 4A phage (and as a clone designated lambda gMHC-1), was shown to code for a cardiac myosin heavy chain of the beta-type. The 5' end of the 14,200-base-pair genomic DNA clone is located in the head region of the myosin chain. The 3' end was shown to extent to the COOH terminus and includes the 3'-nontranslated sequence of the corresponding mRNA. The identification of lambda gMHC-1 as coding for a cardiac beta-myosin heavy chain was achieved by heteroduplex mapping using genomic cardiac myosin heavy-chain DNA of rabbit as a probe and, furthermore, by DNA sequence analysis of three selected subregions of the clones DNA including the 3'-nontranslated sequence. It was demonstrated by the S1 nuclease protection technique that the beta-myosin heavy-chain gene is transcribed in human heart muscle. In addition, we have found by the same technique that it is also expressed in human skeletal muscle.

DNA topoisomerase II cleaves at specific sites in the 5′ flanking region of c-fos proto-oncogenes in vitro

We have analyzed 1 kb of cloned human c-fos sequence (-711 to +287) for calf thymus DNA topoisomerase II cleavage sites in vitro. Using the anti-tumor drug VP16 (demethylepipodophyllotoxin-beta-D-glucoside) with purified topoisomerase II, we identify twelve sites. Five sites are clustered around position -306 in a region that possesses enhancer-like properties. A second cluster of three sites is positioned 15 bp upstream of the TATA promoter element. With a HeLa nuclear extract as a source of topoisomerase II, a subset of cleavage sites is conserved within the two clusters. The cleavage sites in the enhancer-like element are conserved in the homologous region of the murine c-fos. These findings raise the possibility that topoisomerase II is involved in mediation of mitogen-induced c-fos expression.

Scl 70 autoantibodies from scleroderma patients recognize a 95 kDa protein identified as DNA topoisomerase I

Sera of patients suffering from the autoimmune disease progressive systemic sclerosis (PSS) are known to contain autoantibodies which have been reported to recognize a 70 kDa antigenic protein, designated the Scl 70 antigen. By immunoblotting of nuclear extracts from HeLa cells with sera from scleroderma patients we observed that the size of the antigen present in such cells depends on the conditions of antigen isolation. When protease inhibitors were included in the extraction buffer, a 95 kDa protein was identified instead of a 70 kDa protein. When protease inhibitors were omitted, a number of polypeptides in the size range 66 to 95 kDa was found. Furthermore, antibodies which had been affinity purified on the 95 kDa antigen, crossreacted with the 66 to 95 kDa polypeptides. These results suggest that the smaller proteins were degradation products of the 95 kDa antigen. Immunofluorescence studies on PtK-2 cells with the antibody specific for the 95 kDa protein gave staining of nuclei, nucleoli and of chromosomes and the nucleolar organizer region in mitotic cells. Since this distribution of antigens within the nucleus was reminiscent of the intranuclear distribution of DNA topoisomerase I found by others we probed purified DNA topoisomerase I from calf thymus directly with the autoantibodies from PSS patients, and also the 95 kDa antigens of HeLa cell nuclei with antibodies raised against the bovine DNA topoisomerase I. From the crossreaction pattern observed with the different antigens and antibodies we conclude that DNA topoisomerase I is one of the antigenic components against which autoantibodies are formed in scleroderma patients.

Inhibition of calf thymus type II DNA topoisomerase by poly(ADP-ribosylation)

The effect of poly(ADP-ribosylation) on calf thymus topoisomerase type II reactions has been investigated. Unknotting of phage P4 head DNA, and relaxation and catenation of supercoiled PM2 DNA are inhibited. We conclude that the inhibition results from poly(ADP-ribosylation) on the following grounds. Firstly, the enzyme poly(ADP-ribose) (PADPR) synthetase and NAD are required, secondly, the competitive synthetase inhibitor nicotinamide abolishes topoisomerase inhibition, and thirdly, the polymer alone is not inhibitory. The mechanism of inhibition appears to be disruption of the strand cleavage reaction. A topoisomerase-DNA complex can be formed that upon treatment with protein denaturant at low ionic strength results in strand cleavage. The amount of DNA present in such a cleavable-complex progressively decreased following pretreatment of topoisomerase type II with PADPR synthetase and increasing concentrations of NAD. Treatment of the pre-formed complex with NAD and PADPR synthetase had no effect on its salt-induced dissociation. This suggests that either poly(ADP-ribosylation) has no influence on dissociation of topoisomerase, in contrast to association, or topoisomerase is not accessible to the synthetase when bound to DNA. Similar data were obtained with calf thymus type I topoisomerase.

Relaxation of supercoiled phosphorothioate DNA by mammalian topoisomerases is inhibited in a base-specific manner

The nucleotide preferences of calf thymus topoisomerases I and II for recognition of supercoiled DNA have been assessed by the relaxation and cleavage of DNA containing base-specific phosphorothioate substitutions in one strand. The type I enzyme is inhibited to varying degrees by all modified DNAs, but most effectively (by approximately 60%) if deoxyguanosine 5'-O-(1-thiomonophosphate) (dGMP alpha S) is incorporated into negatively supercoiled DNA. A DNA in which all internucleotide linkages of one strand are phosphorothionate is relaxed, most probably via the unsubstituted strand. The type II enzyme is inhibited when deoxyadenosine 5'-O-(1-thiomonophosphate) (dAMP alpha S) or deoxyribosylthymine 5'-O-(1-thiomonophosphate) is incorporated into the DNA substrate, and the course of the relaxation reaction changes from a distributive mode to a predominantly processive mode. A fully substituted DNA is very poorly relaxed by the type II enzyme, illustrating the strict commitment of the enzyme to relaxation via double-strand cleavage. The sense of supercoiling does not affect the inhibition profile of either enzyme. DNA strand breaks introduced by type II topoisomerase in a normal control DNA or deoxycytidine 5'-O-(1-thiomonophosphate)-substituted DNA on treatment with sodium dodecyl sulfate at low ionic strength are prevented by pretreatment with 0.2 M NaCl. In contrast, breaks in DNA having either dAMP alpha S or all four phosphorothioate nucleotides incorporated in one strand are prevented only with higher NaCl concentrations. Thus indicating activity at the phosphorothioate linkage 5' to dA but not 5' to dC. We conclude that topoisomerase II activity occurs preferentially at sites possessing dAMP or dTMP, and that dGMP is involved in DNA recognition by topoisomerase I.

Characterisation of size variants of type I DNA topoisomerase isolated from calf thymus

Calf thymus DNA topoisomerase I, which belongs to the eukaryotic type I topoisomerases, is in a typical preparation purified as a set of five major polypeptides with Mr between 70000 and 100000. At least four of these proteins have binding affinity for DNA as was shown by incubating them with radioactive single-stranded DNA after separation in dodecylsulfate polyacrylamide gels and blotting onto nitrocellulose filters. That these polypeptides have DNA relaxing activity was directly demonstrated with protein extracted from single bands of dodecylsulfate/polyacrylamide gels. We consider the 100000-Mr protein to be the native enzyme. The smaller components are catalytically active fragments of the native topoisomerase most probably arising from limited proteolysis either within the nucleus or during the purification of the enzyme. In two-dimensional non-equilibrium pH-gradient electrophoresis gels the topoisomerase size variants exhibit apparent pI values between 8.1 and 8.3, with small but distinct differences between the components. The calf thymus topoisomerase I, upon binding to phage fd-DNA, protects a stretch of 15-25 nucleotides against digestion with DNase I.

Characterization of a human genomic DNA fragment coding for a myosin heavy chain

A DNA segment from the human genome with information for myosin heavy chain (MHC) was isolated from a human genomic DNA library cloned in lambda Charon 4A phages. The isolation was accomplished by a myosin cDNA probe obtained from rabbit heart muscle mRNA (Sinha et al. 1982). The selected human DNA clone, designated lambda gMHC1, contains a genomic DNA fragment of about 14 kilobase pairs. The transcriptional polarity of this DNA was determined. The 5'-end of the gene is missing from the cloned fragment. This human gene exhibits sequence homology to MHC DNA of rabbit and chicken, but not to an MHC sequence of nematode. The isolated gene fragment is a member of the human MHC multi-gene family, which is presumed to consist of probably more than ten separate sarcomeric MHC genes per haploid genome.

Chromosomal localization of a human myosin heavy-chain gene by in situ hybridization

A cloned rabbit heart muscle myosin heavy-chain cDNA was hybridized in situ with human metaphase chromosomes. The probe was known to have sequence homology with human genomic heavy-chain DNA. Only one site in the human haploid karyotype was labeled with the cDNA, and this site was found on the short arm of chromosome 17. The localization of autoradiographic grains suggests a subregional assignment of the myosin heavy-chain locus to 17p 1,2-pter.

DNA topoisomerase I from calf thymus is inhibited in vitro by poly(ADP-ribosylation)

A slight DNA topoisomerase I activity was detected in highly purified poly(ADP-Rib)polymerase prepared from calf thymus. This copurified activity was found to be suppressed under conditions where the poly(ADP-ribosylation) reaction occurs in the presence of NAD. Purified topoisomerase I from calf thymus was shown to be ADP-ribosylated by poly(ADP-Rib) polymerase purified from the same tissue. Poly(ADP-ribosylation) of topoisomerase I produces an inhibition of the enzymatic activity in parallel to the extent of ADP-ribosylation. The fact that a slight poly(ADP-Rib) polymerase activity was also found to copurify with a topoisomerase I preparation and that topoisomerase I activity can be modified by ADP-ribosylation, may suggest a spatial and functional correlation of these two enzymes in chromatin.

Effect of deoxynucleoside phosphorothioates incorporated in DNA on cleavage by restriction enzymes

DNA synthesized in vitro using deoxynucleoside phosphorothioates as substrates is quite similar to normal DNA in its biochemical properties (Vosberg, H.P., and Eckstein, F. (1977) Biochemistry 16, 3633-3640). In order to investigate the effect of phosphorothioate groups in DNA on the cleavage pattern of restriction endonucleases phosphorothioate double-stranded, circular, replicative form of fd DNA was synthesized in vitro with Escherichia coli DNA polymerase I using native single-stranded DNA as template and mixtures of three normal nucleotides and one nucleoside phosphorothioate analogue as substrates. The double-stranded products were hybrids with respect to their phosphorothioate content. Restriction analysis of normal and phosphorothioate DNA with the restriction endonucleases Hae III, Bam HI, Hpa II, HindII, Alu I, and Taq I showed that the enzymes were inhibited to different degrees depending on which of the nucleotides was replaced by the phosphorothioate. Most significant, inhibition was seen throughout with those DNAs which contained a phosphorothioate exactly at the cleavage site. Phosphorothioate substitutions at other positions, but still within the recognition sequences, were, except for Alu I, not or weakly inhibitory. Phosphorothioate nucleotides not present in the recognition sequences did not affect at all the fragment patterns. The results show that recognition sequences of restriction endonucleases can be selectively protected against cleavage by base-specific introduction of phosphorothioate groups into DNA.

Intracellular distribution of DNA topoisomerase I in fibroblasts from patients with Fanconi's anaemia

The activity of DNA topoisomerase I(DNA nicking-closing enzyme) was analysed in cytoplasmic and nuclear extracts of six independently derived Fanconi and four normal fibroblast cell lines. In all experiments the total cellular activity was predominantly found in the nuclear extracts (88-100%). In addition, a minor proportion of the enzyme (up to 12%) was randomly present in some of the cytoplasmic fractions of both Fanconi and normal fibroblasts. These results indicate that Fanconi's anaemia is probably not due to or accompanied by a maldistribution of topoisomerase I between nuclei and cytoplasm.

Incorporation of phosphorothioate groups into fd and phi X174 DNA

We have synthesized fd and phi X174DNA in the presence of 2'-deoxyadenosine 5'-O-(1-thiotriphosphate) (dATP alpha S) and the corresponding phosphorothioate derivatives of dCTP and dTTP using ether-permeabilized E. coli cells or crude cell extracts of E. coli DNA polymerase I. Reaction rates of enzymes involved in the formation or breakdown of DNA are decreased in the presence of phosphorothioates. The amount of label incorporated with [35S]dATP alpha S suggests that the dAMP has been completely substituted by 2'-deoxyadenosine 5'-0-phosphorothioate (dAMPS). The substituted DNAs have the same sedimentation coefficients, similar buoyant density, infectivity, and thermal stability as the unsubstituted DNAs. The procedure therefore allows specific modification at the 5' position of dA, dC, or dT in the DNA. In view of the recent demonstration of specific binding of Pt2+ complexes to the phosphorothioate analogue of poly[r(A-U)] (Strothkamp, K.G., and Lippard, S.J. (1976), Proc. Natl. Acad. Sci. U.S.A. 73, 2536), the synthesis of phosphorothioate containing DNA may be of use for DNA sequencing by electron microscopy.

Action of nicking-closing enzyme on supercoiled and nonsupercoiled closed circular DNA: formation of a Boltzmann distribution of topological isomers

Highly purified nicking-closing enzyme from mouse cells in 20-fold enzyme/substrate excess converts closed circular native PM2, ColE1, and Minicol DNA into limit product sets of DNAs. Each set has a mean degree of supercoiling of approximately zero. The individual species in the sets differ by deltatau = +/-1, +/-2, etc., and the relative masses fit a Boltzmann distribution. It was also demonstrated that "nonsupercoiled" closed circular duplex molecules serve as substrates for the nicking-closing enzyme, and that a distribution of topological isomers is generated. Polynucleotide ligase, acting on nicked circular DNA, forms under the same conditions, the same set of closed DNAs. The latter enzyme freezes the population into sets of molecules otherwise in configurational equilibrium in solution.

Carcinogen-induced DNA repair in nucleotide-permeable Escherichia coli cells. Induction of DNA repair by the carcinogens methyl and ethyl nitrosourea and methyl methanesulfonate

Ether-permeabilized (nucleotide-permeable) cells of Escherichia coli show excision repair of their DNA after having been exposed to the carcinogens N-methyl-N-nitrosourea (MeNOUr), N-ethyl-N-nitrosourea (EtNOUr) and methyl methanesulfonate (MeSO2OMe) which are known to bind covalently to DNA. Defect mutations in genes uvrA, uvrB, uvrC, recA, recB, recC and rep did not inhibit this excision repair. Enzymic activities involved in this repair were identified by measuring size reduction of DNA, DNA degradation to acid-soluble nucleotides and repair polymerization. 1. In permeabilized cells methyl and ethyl nitrosourea induced endonucleolytic cleavage of endogenous DNA, as determined by size reduction of denatured DNA in neutral and alkaline sucrose gradients. An enzymic activity from E. coli K-12 cell extracts was purified (greater than 2000-fold) and was found to cleave preferentially methyl-nitrosourea-treated DNA and to convert the methylated supercoiled DNA duplex (RFI) of phage phiX 174 into the nicked circular form. 2. Degradation of alkylated cellular DNA to acid solubility was diminished in a mutant lacking the 5' leads to 3' exonucleolytic activity of DNA polymerase I but was not affected in a mutant which lacked the DNA polymerizing but retained the 5' leads 3' exonucleolytic activity of DNA polymerase I. 3. An easily measurable effect is carcinogen-induced repair polymerization, making it suitable for detection of covalent binding of carcinogens and potentially carcinogenic compounds.