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Biomedical subjects

N Arnheim

Publications and source records attributed to N Arnheim.

At least 127 records · Page 7Linked to original sources
PubMed1980

5' flanking region of immunoglobulin heavy chain constant region genes displays length heterogeneity in germlines of inbred mouse strains.

Genomic Southern blotting analysis reveals that a 5' flanking DNA sequence located 1.5-2.0 kb upstream from the C mu and C alpha genes undergoes extensive length variation in the germlines of inbred and wild mice. In addition, genomic clones of the BALB/c C mu gene undergo deletion events during their propagation in Charon 4A when maintained in RecA+ bacterial strains. These deletion events occur between the JH cluster and the C mu gene and approximately 2.0 kb 5' of the C alpha gene, and may encompass several kb of DNA. Deletion events are capable of yielding a group of C mu clones which differ in size by units of 100-200 bp. The site of length variation in the mouse germline corresponds to the location of these cloning-derived deletion events, suggesting that both phenomena are reflections of intrinsic genetic properties of these Ig gene 5' flanking sequences.

Animals↗
PubMed1980

Mitochondrial DNA polymorphism: evidence that variants detected by restriction enzymes differ in nucleotide sequence rather than in methylation.

Restriction enzyme analysis of mtDNAs for the purpose of determining sequence divergence rests on the assumption that variant recognition sites differ with respect to sequence and not methylation. This assumption was tested on two mtDNAs, A and B, which are distributed throughout the laboratory rat population and which can be distinguished by a number of restriction enzymes. The mtDNAs were cloned and the nucleotide sequences of corresponding small HindIII fragments, in which a variant EcoRI site occurs, were determined. Evidence that the fragments differ in sequence and not methylation is as follows: (i) The cloned mtDNA yielded the same fragment pattern as did native mtDNA when treated with EcoRI, Hha I, HinfI, and Hae III; (ii) three nucleotide replacements were found in the 169-base pair fragment, A.T in equilibrium G.C, A.T in equilibrium G.C, T.A in equilibrium G.C; (iii) one of these replacements, A.T in equilibrium G.C at position 80, accounts for the presence of the EcoRI site in the type A and its absence in the type B mtDNA. Examination of the sequence leads to the suggestion that these three nucleotide replacements are silent; i.e., they would not lead to amino acid substitutions in a possible encoded protein.

Animals↗
PubMed1980

Molecular evidence for genetic exchanges among ribosomal genes on nonhomologous chromosomes in man and apes.

We have found that human and ape ribosomal genes undergo concerted evolution involving genetic exchanges among nucleolus organizers on nonhomologous chromosomes. This conclusion is based upon restriction enzyme analysis of the ribosomal gene families in man and five ape species. Certain structural features were found to differ among (but not within) species even though the ribosomal genes have a multichromosomal distribution. Genetic exchanges among nucleolus organizer regions may be related to the well-known phenomenon of acrocentric chromosome associations observed in man and apes. Length variation in a region of the nontranscribed spacer was found in both chimpanzee species we examined. The nature of this length variation was found to be identical to that previously described in man. The origin of the length variation and its polymorphism within these three species might be explained by unequal alignment and unequal cross-over among the ribosomal genes. An especially surprising finding was a nucleotide sequence polymorphism present in each individual human and ape we examined. Some ribosomal genes of each individual have a HindII site in the 28S gene about 800 base pairs from the EcoRI site in this gene. The remaining 28S genes lack this HindII site. The presence of this polymorphism within individuals of every species we examined suggests that it has been maintained by natural selection.

Animals↗
PubMed1979

Biochemical characterization of "LAP," a polymorphic aminopeptidase from the blue mussel, Mytilus edulis.

A genetically variable naphthylamidase enzyme, previously described as "leucine aminopeptidase," was purified approximately fiftyfold, and its biochemical properties were investigated. The enzyme was renamed "aminopeptidase I." Substrate affinities demonstrate that it is an alpha-aminoacyl peptide hydrolase (E.C. 3.4.11.-). Aminopeptidase I had a monomer molecular weight of 65--68,000, average of pI of pH 4.88, and broad pH optima between 6.5 and 8.0. The enzyme was inactivated rapidly between 40 and 50 C. Antibodies from purified enzyme did not cross-react with other naphthylamidases, but aminopeptidase I activity was inhibited by immune serum. The enzyme exhibited highest naphthylamidase activity for aromatic and hydrophobic aminoacyl naphthylamides. Aminopeptidase activity was highest for aromatic and hydrophobic N-terminal residues of tripeptides. Certain divalent metal cations, p-OH-mercuribenzoate, and N-ethylmaleimide were strongly inhibitory while chelating agents activated the enzyme.

Aminopeptidases↗
PubMed1979

Characterization of mouse ribosomal gene fragments purified by molecular cloning.

Four mouse ribosomal gene fragments cloned in lambda gtWES were studied by restriction enzyme mapping and Southern transfer experiments. These fragments were found to contain 18S DNA and transcribed as well as non-transcribed spacer DNA. Variation in the structure of these mouse DNA inserts was limited to one region of spacer DNA. This variation may reflect real structural differences found in mouse ribosomal genes or possibly deletion events which occurred during cloning. The transcribed regions of the inserts appear identical to one antoher and restriction enzyme fragments from this region correspond to fragments observed in digests of total mouse DNA. These clones will be useful in studying the structure of transcribed spacer DNA including the ribosomal gene promoter.

Animals↗
PubMed1978

Incomplete dosage compensation in an evolving Drosophila sex chromosome.

Cellular autoradiography was used to measure relative rates of chromosomal RNA synthesis and to examine the regulatory phenomenon of X-linked dosage compensation in Drosophila miranda, a species containing two distinct, nonhomologous X chromosomes (X1 and X2). The X1 chromosome was found to be dosage-compensated, since the rate of RNA synthesis along the single X1 chromosome in males equaled that of both X1 chromosomes in females. Unlike other sex chromosomes that have been studied, the more recently evolved X2 heterochromosome exhibited regional differences in transcriptional activity when males and females were compared. The distal 10% of the X2 was not dosage-compensated, whereas the majority of an interior segment, representing 30% of the X2 chromosome's length, was found to be dosage-compensated. Our data are consistent with the idea that the evolution of X2 dosage compensation has paralleled the differentiation of the X2 sex chromosome. In addition, gene rearrangement seems to have accompanied the acquisition of a dosage-compensory mechanism in the X2.

Animals↗
PubMed1977

Heterogeneity of the ribosomal genes in mice and men.

The structures of mouse and human ribosomal DNA were studied using the restriction enzymes Eco R1 and Hind III. Individual mice or humans showed a heterogeneous pattern of restriction fragments resulting from differences in the non-transcribed spacer DNA. Six individual mice from the inbred strain CBA/H-T6 had identical patterns. The same pattern was shown by another CBA strain and by C3H. These strains were originally derived from a BALB X DBA cross made in 1920. Different patterns were found for BALB/c, C57BL and Mus poschiavinus. Cultured cells derived from C3H mice (L cells) showed a pattern quantitatively different from that of the parent strain, but two myeloma cell lines derived from BALB/c showed the same pattern as BALB/c mice. Ribosomal DNA in man is also heterogeneous. Differences were observed between human DNAs in the amounts of the different spacer classes. Studies on mouse-human cell hybrids suggest that some spacer classes are present on more than one of the five human nucleolus organizers.

Animals↗
PubMed1976

Preparation of specific antisera to Drosophila acid phosphatase without rigorous protein purification.

Extracts from an acid phosphatase CRM- null mutant of Drosophila melanogaster were used to eliminate contaminating antibodies in a nonspecific preparation of anti-acid phosphatase serum. This method of producing specific antisera makes unnecessary the rigorous purification of an antigen prior to immunization attempts in those cases where CRM- null mutants of the antigen are available. Antisera so prepared could be used for a wide variety of purposes.

Acid Phosphatase↗
PubMed1974

Isozymes of lysozyme in leukocytes and egg white: evidence for the species-specific control of egg-white lysozyme synthesis.

Two structurally distinct forms of eggwhite lysozyme (EC 3.2.1.17) are known. The egg white of some species contains both of these forms, while the egg white of other species appears to contain only one or the other of them. We have immunological and electrophoretic evidence that the chicken, which has only one lysozyme type in its egg white, contains both types in its polymorphonuclear leukocytes. Experiments on Embden goose bone marrow showed that this tissue also contains both lysozymes, even though the egg white of this species contains only one of them. Our studies suggest that many avian species have the genetic loci that code for both forms of lysozyme, but that a species-specific regulatory mechanism controls whether one or the other or both of them are expressed during egg white production. The fact that two distinct lysozymes are present in chicken leukocytes may be of significance to the antibacterial mechanism of these cells, especially in light of the fact that they lack myeloperoxidase, an important leukocyte enzyme in mammals.

Animals↗