Language and cognition in children with metachromatic leukodystrophy: onset and natural course in a nationwide cohort

Background

Metachromatic leukodystrophy (MLD) is a rare, genetic neurodegenerative disease. It leads to progressive demyelination resulting in regression of development and early death. With regard to experimental therapies, knowledge of the natural course of the disease is highly important. We aimed to analyse onset and character of first symptoms in MLD and to provide detailed natural course data concerning language and cognition.

Methods

Patients with MLD were recruited nationwide within the scope of the German research network LEUKONET. 59 patients’ questionnaires (23 late-infantile, 36 juvenile) were analysed.

Results

Time from first symptoms (at a median age of 1.5 years in late-infantile and 6 years in juvenile MLD) to diagnosis took one year in late-infantile and two years in juvenile patients on average. Gait disturbances and abnormal movement patterns were first signs in all patients with late-infantile and in most with juvenile MLD. Onset in the latter was additionally characterized by problems in concentration, behaviour and fine motor function (p = 0.0011, p < 0.0001, and p = 0.0012). Half of late-infantile patients did not learn to speak in complete sentences after an initially normal language acquisition. They showed a rapid language decline with first language difficulties at a median age of 2.5 years and complete loss of expressive language within several months (median age 32, range 22–47 months). This was followed by total loss of communication at a median age of around four years. In juvenile patients, language decline was more protracted, and problems in concentration and behaviour were followed by decline in skills for reading, writing and calculating around four years after disease onset.

Conclusions

Our data reflect the natural course of decline in language and cognition in late-infantile and juvenile MLD in a large cohort over a long observation period. This is especially relevant to juvenile patients where the disease course is protracted and prospective studies are hardly feasible. Knowledge of first symptoms may lead to earlier diagnosis and subsequently to a better outcome following therapeutic intervention. Our data may serve as a reference for individual treatment decisions and for evaluation of clinical outcome after treatment intervention.

GM2 gangliosidosis in an adult pet rabbit

A 1.5-year-old neutered male rabbit was presented with chronic nasal discharge and ataxia. Rapid progression of neurological signs was noted subsequent to general anaesthesia and the rabbit was humanely destroyed due to the poor prognosis. At necropsy examination there were no gross changes affecting the brain or spinal cord. Microscopical examination revealed that the perikarya of numerous neurons in the brain and spinal cord were distended by the intracytoplasmic accumulation of pale, finely granular to vacuolar material. Transmission electron microscopy showed this to be composed of concentric membranous cytoplasmic bodies. Thin layer chromatography revealed elevation of GM2 ganglioside in the brain of this rabbit compared with that of an unaffected control rabbit. Enzymatically, there was markedly reduced activity of tissue β-hexosaminidase A in brain and liver tissue from the rabbit. This was a result of an almost complete absence of the enzymatic activity of the α-subunit of that enzyme. These findings are consistent with sphingolipidosis comparable with human GM2 gangliosidosis variant B1.

In vitro analysis of multipotent mesenchymal stromal cells as potential cellular therapeutics in neurometabolic diseases in pediatric patients

Multipotent mesenchymal stromal cells (MSCs) play an important role in stromal support for hematopoietic stem cells, immune modulation, and tissue regeneration. We investigated their potential as cellular therapeutic tools in neurometabolic diseases as a growing number of affected children undergo to bone marrow transplantation. MSCs were isolated from bone marrow aspirates and expanded ex vivo under various culture conditions. MSCs under optimal good medical practice (GMP)-conform culture conditions showed the typical morphology, immunophenotype, and plasticity. Biochemically, the activities of beta-hexosaminidase A, total beta-hexosaminidase, arylsulfatase A (ASA), and beta-galactosidase measured in MSCs were comparable to those in fibroblasts of healthy donors. These four enzymes were interesting for their expression in MSCs, as each of them is defective, respectively, in well-known neurometabolic diseases. We found that MSCs released significant amounts of ASA into the media. In coculture experiments, fibroblasts from patients with metachromatic leukodystrophy, who are deficient for ASA, took up a substantial amount of ASA that was released into the media from MSCs. Mannose-6-phosphate (M6P) inhibited this uptake, which was in accordance with the M6P receptor-mediated uptake of lysosomal enzymes. Taken together, we show that MSCs produce appreciable amounts of lysosomal enzyme activities, making these cells first-choice candidates for providing metabolic correction when given to enzyme-deficient patients. With the example of ASA, it was also shown that an enzyme secreted from MSCs is taken up by enzyme-deficient patient fibroblasts. Given the plasticity of MSCs, these cells represent an interesting add-on option for cellular therapy in children undergoing bone marrow transplantation for lysosomal storage diseases and other neurometabolic diseases.

Niemann-Pick disease type A and B are clinically but also enzymatically heterogeneous: pitfall in the laboratory diagnosis of sphingomyelinase deficiency associated with the mutation Q292 K

This study describes a diagnostic pitfall in the laboratory diagnosis of patients with sphingomyelinase deficiency (SMD; Niemann-Pick disease types A and B; NPA and NPB), in cases where sphingomyelinase activity was not determined with sphingomyelin as the natural enzymic substrate. Four of 24 SMD patients studied had falsely normal or enhanced activity, when a so-called artificial sphingomyelinase substrate, 2-N-(hexadecanoyl)-amino-4-nitrophenyl phosphorylcholine (HNP), was used, whereas SMD was clear with the sphingomyelin substrate. Those four patients had the Q292 K mutation of the acid sphingomyelinase gene (SMPD1) on at least one allele. Three of the four patients (no data available from one) experienced only late-infantile or juvenile, though distinct, neurological involvement, where learning disabilities, hypo- or areflexia or mild ataxia were initial signs. The laboratory pitfall with HNP substrate, which is used in many laboratories, raises the risk that some SMD patients are overlooked, and it prevents the consideration of a late-manifesting neurological course in some patients as well as the planning of enzyme substitution therapy in non-neurological SMD (NPB) patients. Since classical NPB is very rare, it is suggested that SMD patients with late- or mild-manifesting neurological symptoms should better be assigned to additional SMD subgroups than grouped with NPB.

NPC1: Complete genomic sequence, mutation analysis, and characterization of haplotypes

Niemann-Pick type C disease (NP-C) is a rare, autosomal recessive lipid storage disorder. At least 96% of all NP-C patients link to NPC1 which encodes for a lysosomally-targeted protein. We describe the complete genomic sequence of 57,052 kb corresponding to the transcribed region of human NPC1 including several exonic and intronic single nucleotide polymorphisms (SNPs). Sequencing of all exons, splice sites, and the promoter region of NPC1 in 12 unrelated Caucasian NP-C patients revealed nine novel and four known most likely disease-causing mutations. Ten unique mutations found only once in 24 disease alleles were observed in patients being compound heterozygous for two different mutations. Two of the three missense mutations identified more than once were observed in a total of four patients homozygous for the respective mutation along with homozygosity for the underlying haplotype. The patients were offspring of most likely nonconsanguineous couples. Based upon genotyping exonic SNPs c.2572A>G (I858V; g.45020A>G) and c.2793C>T (N931N; g.45686C>T) and segregation analysis we characterized the haplotype of all 24 NPC1 alleles and of 138 alleles of healthy Caucasian control subjects. All four permutations between the two SNPs were identified in the control alleles: 2572A-2793C (50%), 2572G-2793T (41%), 2572G-2793C (5%), and 2572A-2793T (4%). These data are suggestive for an ancestral intragenic recombination within a genomic fragment of <666 bp. While 17 of 24 NP-C alleles (71%) shared haplotype 2572G-2793T, this haplotype accounted for only 41% in the controls (p=0.007; 2-sided Fisher exact test) suggesting the possibility of an influence of the haplotypic background on expression of missense mutations in NPC1.

Quantified increases of cholesterol, total lipid and globotriaosylceramide in filipin-positive Niemann-Pick type C fibroblasts

BACKGROUND

Niemann-Pick disease type C (NPC) is a neurovisceral lysosomal lipidosis caused in most cases by mutations in the NPC1 gene that codes for the cholesterol regulating NPC1 protein.

METHODS

Cultured skin fibroblasts from 11 NPC patients aged 0.25 to 34 years at diagnosis with different severity of neurologic and visceral involvement, diagnosed by the cytochemical filipin test for lysosomally stored cholesterol, were analyzed for lipid composition. Cholesterol and other lipids were separated on thin-layer chromatography from fibroblast total lipid extracts, quantified by densitometry and compared with the total cell lipid mass.

RESULTS

Cholesterol concentration in the patient cells was 1.5 to 5-fold higher than normal and total lipids up to 2.4-fold normal. Cholesterol and total lipids were particularly high in cells from NPC patients aged less than about 6 years, and for the whole patient series the abundance of fibroblast cholesterol was correlated with the tentatively assessed clinical disease severity. The findings in NPC suggested that NPC1 protein has a role not only in the balance of cholesterol but also the distribution of the total cell lipid mass. Another increase found in the NPC cells was that of a minor lipid fraction, globotriaosylceramide (Gb3, known as a cell signalling glycolipid). Gb3, in the average of its very variable individual concentrations, was about 2.5-fold higher in the NPC cell group as compared to normal or pathologic control group, but there was no correlation of Gb3 with the other lipid concentrations studied.

CONCLUSIONS

For NPC diagnosis, the fibroblast cholesterol and total lipid quantification can be used as an alternative to the usual filipin test for lysosomal cholesterol, but both test methods are prone to equivocal results in cells from a small fraction of atypical NPC patients, where chemical testing in organ biopsies or mutational analysis of the NPC1 gene should be tried.

Progressive cerebellar ataxia, proximal neurogenic weakness and ocular motor disturbances: hexosaminidase A deficiency with late clinical onset in four siblings

Tay-Sachs disease is a genetically determined neurodegenerative disorder, resulting from mutations of the hexosaminidase (Hex) A gene coding for the alpha-subunit of beta-D-N-acetyl-hexosaminidase. Clinically, there is severe encephalomyelopathy leading to death within the first few years of life. Hex A activity is usually absent in tissue and body fluids of these patients. Juvenile and adult Hex A deficiencies are less severe but rare variants with some residual Hex A activity. All these variants are most prevalent among Ashkenazi Jews. We describe a non-Jewish family in which four adult brothers and sisters had markedly reduced Hex A activities and onset of symptoms in the second decade of life. The phenotypical expression was remarkably homogeneous, consisting in a combination of slowly progressive motor neuron disease, ataxia and ocular motor disturbances. None of the patients were demented at this stage of their illness. Magnetic resonance studies showed severe cerebellar atrophy, but were otherwise normal. Hex A deficiency was established by biochemical measurements in the serum and skin fibroblasts using the fluorogenic substrates 4-MUG and 4-MUGS as well as by gel electrophoresis. Molecular genetic studies revealed that the patients are compound heterozygotes for the 'adult' mutation Gly269 --> Ser and the 'infantile' 4-base insertion in exon 11 of the Hex A gene.

Leptomeningeal lipid storage patterns in Fabry disease

We found two patterns of leptomeningeal storage that reflect two basic visceral storage patterns in Fabry disease. (i) A generalized-type leptomeningeal storage pattern, affecting all main leptomeningeal cell types (external arachnoideal epithelium, fibroblasts, vessel wall elements), was a consistent finding in three cases of classical generalized visceral phenotype. (ii) A localized leptomeningeal storage pattern was expressed, to a high degree, solely in the external arachnoidal epithelium; this pattern was found in one case with the variant visceral-restricted-type storage (confined to the cardiocytes). Thus, the external arachnoidal epithelium may be particularly susceptible to Fabry lipid storage, probably caused by a distinctly larger sustained lysosomal lipid load as compared to other cell types.

Additional biochemical findings in a patient and fetal sibling with a genetic defect in the sphingolipid activator protein (SAP) precursor, prosaposin. Evidence for a deficiency in SAP-1 and for a normal lysosomal neuraminidase

It has been shown that sphingolipid activator proteins (SAPs) 1 and 2 are encoded on the same gene along with two other putative activator proteins [Fürst, Machleidt & Sandhoff (1988) Biol. Chem. Hoppe-Seyler 369, 317-328 and O'Brien, Kretz, Dewji, Wenger, Esch & Fluharty (1988) Science 241, 1098-1101]. We have undertaken further biochemical investigations on a patient and fetal sibling, who were previously shown to have a unique sphingolipid storage disorder associated with an SAP-2 deficiency [Harzer, Paton, Poulos, Kustermann-Kuhn, Roggendorf, Grisar & Popp (1989) Eur. J. Pediatr. 149, 31-39]. The severity of their disorder suggested that other products of the SAP precursor or prosaposin gene may also be deficient. The turnover of cerebroside sulphate and globotriaosylceramide were investigated and were both impaired in fibroblasts from the patient and fetus. However, the activities of cerebroside sulphate sulphatase and globotriaosylceramide alpha-galactosidase in vitro were normal in cells from the fetus and patient respectively. In addition, there was an increase in cerebroside sulphate concentration in the kidney of the affected fetus. These results indicate that, in addition to the SAP-2 deficiency, there was a defect in SAP-1 function in this disorder. Additional increases in the concentration of monohexosyl- and dihexosyl-ceramide in the fetal kidney probably reflect the deficiency of SAP-2 in the case of monohexosylceramides, and the combined activator deficiency in the case of dihexosylceramides. Lactosylceramide-loading studies confirmed that there was a defect in the turnover of this lipid in fibroblasts from the affected patient and fetus but not from a patient with an isolated SAP-1 deficiency, or from patients with Krabbe disease, GM1 gangliosidosis or galactosialidosis. It has been suggested [Potier, Lamontagne, Michaud & Tranchemontagne (1990) Biochem. Biophys. Res. Commun. 173, 449-456] that the prosaposin gene also codes for lysosomal neuroaminidase. However, we found normal neuraminidase activity in fibroblasts from our patient, using assay conditions which are diagnostic for sialidosis patients. The role of prosaposin gene products in sphingolipid metabolism is discussed in view of our biochemical findings in this genetic disorder.

Sphingolipid activator protein 1 deficiency in metachromatic leucodystrophy with normal arylsulphatase A activity. A clinical, morphological, biochemical, and immunological study

A 7-year-old boy had clinical features of metachromatic leucodystrophy (MLD), however, an increased urinary sulphatide excretion was found in the presence of normal arylsulphatase A (and alpha-galactosidase A) activity. A rectal biopsy showed metachromatically staining storage macrophages as well as nonmetachromatic, but PAS-positive, submucosal neurons filled with membranous cytoplasmic bodies. These two types of storage material led to testing for a sphingolipid activator protein (SAP) deficiency. Loading tests with sulphatide and globotriaosylceramide showed deficient turnover of both sphingolipids in cultured fibroblasts. Using the Ouchterlony method, there was no reactivity between a described anti-SAP 1 antiserum and the patient's fibroblast extracts. This new case of SAP-1 deficient MLD was compared with the four cases of this variant known from the literature. Our results indicate that rectal biopsy morphology and lipid loading biochemistry should prove useful for the screening of SAP defects.

Cardiocyte storage and hypertrophy as a sole manifestation of Fabry's disease. Report on a case simulating hypertrophic non-obstructive cardiomyopathy

Fabry's disease was diagnosed in an adult patient as a lipid storage-induced non-obstructive hypertrophic cardiomyopathy. Stable angina pectoris started 15 years before death, was followed by slowly progressive heart failure and repeated pulmonary thromboembolism with death at 63 years. Autopsy disclosed enormous cardiomegaly (1100 g), cardiac storage of ceramide trihexoside (CTH) of the same intensity as in classical cases of generalized Fabry's disease (11 mg lipid/g wet weight) restricted to cardiocytes. Other tissues (liver, kidney, brain, pancreas, pulmonary artery, coronary arteries) were free of storage. Using proton magnetic resonance analysis on formaldehyde-fixed tissue the stored CTH was identified as globotriaosylceramide. It was enzymatically degradable by control cell cultures but left uncleaved by mutant reference Fabry cells. Alpha-galactosidase activities in peripheral leucocytes of all four of the patient's daughters were in the heterozygous range. The diagnostic difficulties in this monosymptomatic novel variant of Fabry's disease are stressed.

Sphingolipid activator protein deficiency in a 16-week-old atypical Gaucher disease patient and his fetal sibling: biochemical signs of combined sphingolipidoses

We describe a patient who presented shortly after birth with hyperkinetic behaviour, myoclonia, respiratory insufficiency and hepatosplenomegaly. Gaucher-like storage cells were found in bone marrow. A liver biopsy showed massive lysosomal storage morphologically different to that in known lipid storage disorders. Biochemically, the patient had partial deficiencies of beta-galactocerebrosidase, beta-glucocerebrosidase and ceramidase in skin fibroblast extracts, but the sphingomyelinase activity was normal. Glucosyl ceramide and ceramide were elevated in liver tissue. Loading of cultured fibroblasts with radioactive sphingolipid precursors indicated a profound defect in ceramide catabolism. Immunological studies in fibroblasts showed a total absence of cross-reacting material to sphingolipid activator protein 2 (SAP-2). The patient died at 16 weeks of age. The fetus from his mother's next pregnancy was similarly affected. The possibility that the disorder results from a primary defect at the level of SAP-2 is discussed. We have named this unique disorder SAP deficiency.

A case of combined Farber and Sandhoff disease

We describe a patient with the biochemically established combination of Farber and Sandhoff disease. A 6-month-old girl of consanguineous Turkish parents presented with hoarseness, stridor, scattered skin nodules, painful swelling of hand joints and ankles, and cherry-red macular spots. Until the age of 2 years her motor and physical condition deteriorated distinctly, however her mental state remained unchanged. A biopsied skin nodule disclosed lysosomal inclusions within storage cells that were typical of Farber disease (curved tubular structures). However, other inclusions (e.g. zebra bodies) were also found. Biochemical findings included ceramide accumulation in skin nodules and cultured fibroblasts, impaired ceramide degradation on loading of cultured fibroblasts with radioactive sphingomyelin, profoundly decreased ceramidase activity in fibroblasts as well as total beta-hexosaminidase activity in fibroblasts and serum, absent hexosaminidase A and B bands on cellogel zymograms, increased urinary oligosaccharide excretion of the Sandhoff disease type, and a partial reduction of ceramidase and total beta-hexosaminidase activities in fibroblasts from her father. A diagnosis of combined Farber and Sandhoff disease was made. The effect of both enzyme deficiencies on the clinical manifestations in this patient and the genetic basis of this combination require further studies.

B1 variant of GM2 gangliosidosis in a 12-year-old patient

A girl aged 12 y, 9 mo, suffered from a progressive neurodegenerative disorder marked by ataxia, extrapyramidal symptoms, and convulsions. A skin biopsy showed axonal pathology that emphasized axonal segments enlarged by mitochondria, dense bodies, and lysosomal residual bodies of the membranous cytoplasmic body type. This ultrastructural pathology suggested GM2 gangliosidosis which was shown to be a B1 variant by specific biochemical studies, although conventional techniques had failed to detect GM2 gangliosidosis. The B1 variant is marked by a deficient activity of beta-hexosaminidase A towards one substrate, and by an almost normal activity towards another. Both parents showed a diminished activity towards the sulfated substrate, suggesting a heterozygous state, and almost normal activity with the second substrate type.

Mitochondrial myopathies with necrotizing encephalopathy of the Leigh type

Two patients with mitochondrial encephalomyopathy (MEP) serve to emphasize the variability of this group of diseases. Cerebral insults, mitochondrial cardiopathy, relapsing ileus, cerebral angioma, ataxia, and myoclonic seizures characterized the first case of an adult man with similar diseases in his family, interpreted as transitional form between mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) and myoclonus epilepsy associated with ragged red fibers (MERRF). The second patient, a floppy infant with cardiomyopathy and myoclonism, statomotoric and mental retardation showed combined defects in mitochondrial respiratory chain at NADH-CoQ reductase and cytochrome c oxidase and a deficiency of carnitine. In both patients neuropathologically criteria of Leigh's syndrome could be demonstrated in the cerebral cortex, in case 2 also clinically. The classificatory problems of the relationships between KSS, MELAS, MERRF, Leigh's as well as Alpers' syndromes are discussed.

Brain galactolipid content in a patient with pseudoarylsulfatase A deficiency and coincidental diffuse disseminated sclerosis, and in patients with metachromatic, adreno-, and other leukodystrophies

A 4-year old boy died of diffuse disseminated sclerosis (DDS) of the brain and was found to have also pseudoarylsulfatase A deficiency (PASAD) with about 20% residual arylsulfatase A (ASA) and cerebroside sulfatase (CS) activity. The reexamination of lipids did not show any sulfatide accumulation in the patient's organ extracts. Although the residual CS activity in the patient's extracts was clearly demonstrable only after partial purification, it was concluded that this activity protects organ tissues from sulfatide accumulation in PASAD, since in sulfatide lipidosis (metachromatic leukodystrophy, MLD) no residual CS activity was detectable. The study of residual ASA activity in the patient's fibroblasts by gel electrofocusing resulted in an almost normal enzyme microheterogeneity. However, the detailed study of the brain galactolipids in the patient revealed an elevated ratio of sulfatide/galactocerebroside content, despite the decrease of both lipids. In tissues of other patients with severe demyelinating diseases different from DDS and MLD, this galactolipid ratio was also found to be increased, especially in three patients with adrenoleukodystrophy. A general mechanism of this anomaly in severe demyelination is considered.

Pyruvate dehydrogenase activity is not deficient in the brain of three autopsied cases with Leigh disease (subacute necrotizing encephalomyelopathy, SNE)

In autopsied brain tissue from three cases with Leigh disease (subacute necrotizing encephalomyelitis, SNE) and controls, the activity of pyruvate dehydrogenase complex (PDHC) was determined under different conditions. It was found to be at the control level or increased, but not deficient. The activities of succinate dehydrogenase, fumarase, succinate cytochrome c reductase, cytochrome c oxidase, and glutamate dehydrogenase were measured as additional mitochondrial markers and showed no essential differences between SNE and control tissue. The metabolic defect in SNE remains unknown. According to the literature, the defect may be localized to the mitochondrial systems. However, the reported results indicate that it cannot be ascribed to PDHC function. Extensive biochemical studies are necessary for understanding of the pathogenesis in the fatal genetic metabolic disease.

Prenatal diagnosis of Tay-Sachs disease. Reflectometry of hexosaminidase A, B, and C/S bands on zymograms

Hexosaminidase (Hex) A, B, and C/S were electrophoretically separated from cultured amniotic fluid cells, fetal brain, and white blood cells. Photographs of cellulose acetate zymograms were evaluated by reflectometric scanning. The usefulness and limitations of this rapid method were shown. Hex A was completely absent in the amniotic fluid cells of one out of three pregnancies at risk for Tay-Sachs disease, but Hex C/S was present in this case. The prenatal diagnosis of Tay-Sachs disease was made, and confirmed with the fetal material after abortion. Hex C/S was distinguishable from a residual or "heterozygous" Hex A activity. In the two other risk pregnancies, reflectometric Hex A activities were found to be 50 and 34% of control; the heterozygous stage was presumed for the fetuses.

Expression and processing of bacterial beta-lactamase in the yeast Saccharomyces cerevisiae

The mode of expression in Saccharomyces cerevisiae of the bacterial antibiotic resistance gene coding for beta-lactamase (EC 3.5.2.6) is described. Yeast transformants, containing hybrid plasmid pMP78-1 consisting of pBR325 in a 2-micrometers DNA vector, synthesize an active beta-lactamase protein. The enzyme was purified about 100-fold over crude extracts. With regard to activity, molecular weight, and binding to specific antibodies the yeast beta-lactamase was indistinguishable from the purified enzyme from Escherichia coli. Because the bacterial enzyme is synthesized as a preprotein with subsequent maturation, the results suggest that S. cerevisiae is able to convert the preprotein to the mature beta-lactamase. This was confirmed by in vitro experiments showing that the bacterial preprotein can be processed by crude extracts of S. cerevisiae.

Inheritance of multiple drug resistance in Saccharomyces cerevisiae: linkage to leu1 and analyses of 2 micron DNA in partial revertants

The inheritance and phenotype of multiple drug resistance in independent multiple drug resistant mutants, two isolated in this laboratory (GR359 and 2-20), and two (DRI 9/T7 and DRI 9/T8) reported by Guerineau et al. (Biochem. Biophys. Res. Commun. 61,462), was investigated. Comparison of resistance to 12 selected drugs showed that the resistance phenotypes of all mutants were similar, although some differences in levels of resistance of each mutant was observed with certain drugs. Mapping of the resistance loci in GR359 and 2-20 revealed tight linkage of both resistance genes to the centromere linked gene leul. 2 micron DNA was analysed by hybridization of 2 micron RNA to EcoRI fragments of a total DNA extract. Eight partial revertants of 2-20, which had been chosen as having a phenotype similar to the 2 micron DNA deficient [cir degrees] isolate DRI 9/T7, revealed the presence of 2 micron DNA. The lack of detectable 2 micron DNA in DRI 9/T7 was confirmed.

Characterization of 2-mum DNA of Saccharomyces cerevisiae by restriction fragment analysis and integration in an Escherichia coli plasmid

Electrophoretic analysis of EcoRI and HindIII restriction fragments of 2-mum supercoiled DNA of Saccharomyces cerevisiae indicated that this class of DNA is heterogeneous and probably consists of two types of molecules. Integration of the 2-mum yeast DNA in E. coli plasmid pCR1 directly showed that existence of two types of molecules as each of these could be individually inserted into separate bacterial plasmids. The difference between the two types of 2-mum circles is due to an inversion of about 1.6 X 10(6) daltons. The inversion is flanked by a reversed duplicated sequence of 0.45 X 10(6) daltons. Possible implications of this structure are dicussed.

Synthesis of high molecular weight polypeptides in Escherichia coli minicells directed by cloned Saccharomyces cerevisiae 2-micron DNA

The minicell-producing Escherichia coli strain P 678-54 was transformed with a series of defined PTY chimeric plasmids consisting of yeast 2-micron DNA and E. coli plasmid pCR1. In minicells the integrated 2-micron DNA from yeast directed specifically the synthesis of six polypeptides with apparent molecular weights of 15,000, 17,500, 20,000, 22,000, 37,000, AND 48,000. The specificity of five other polypeptides, which cover a molecular weight range of 19,000 to 28,000, has not yet been established with certainty. Neither the orientation of the integrated DNA, nor the inversion which distinguishes the two structural forms of 2-micron DNA affected the polypeptides synthesized. However, integration at a given EcoRI site appeared to be correlated with the absence of one particular polypeptide band; this suggests that at least one of these sites is located in an expressed region of the DNA.