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Biomedical subjects

U Wobus

Publications and source records attributed to U Wobus.

53 records · Page 3Linked to original sources
PubMed1984

Balbiani ring DNA: sequence comparisons and evolutionary history of a family of hierarchically repetitive protein-coding genes.

All known types of Balbiani ring (BR) genes consist of multiple, tandemly arranged, ca. 180 to 300-bp repeat units that can be divided into a constant region and a subrepeat region. The latter region includes short tandem subrepeats (SRs). Comparison of all available BR sequences using computer methods has enabled us (a) to define more precisely the constant and subrepeat regions, (b) to infer the evolutionary relationships among the various types of BR repeats, (c) to derive a consensus approximation of an ancestral sequence from a small segment of which the highly diverse present-day SRs may have originated, and (d) to detect an underlying substructure in the constant region, evident in the consensus but not in the present-day sequences and possibly corresponding to an original 39-bp DNA segment from which the extant, giant BR sequences may have evolved. We discuss the processes of reduplication, diversification, and homogenization within the hierarchically repetitive BR sequences as examples of how a simple DNA element may evolve into a diverse family of large, protein-coding genes.

Animals↗
PubMed1982

The basic repeat unit of a Chironomus Balbiani ring gene.

A clone derived from the Balbiani ring b (BRb) gene of Chironomus thummi has been used to study the internal organization of that gene. Much of the gene consists of approximately 80 copies of a ca. 300 bp repeat unit, which are tandemly organized. The BRb clone contains a major part of that unit (242 bp). Sequence analysis shows that approximately 60% of the unit corresponds to short, tandemly organized subsequences, which encode peptides 8 to 11 residues long. In turn, each subsequence consists of even shorter internal repeats, corresponding to a tripeptide (consensus Proline. Serine. Lysine.). The remainder of the ca. 300 bp unit probably does not have obvious repetitive substructure.

Animals↗
PubMed1982

Characterization of a 249-bp tandemly repetitive, satellite-like repeat in the translated portion of Balbiani ring c of Chironomus thummi.

A major part of Balbiani ring (BR)c DNA of Chironomus thummi consists of tandem 249-bp repeats which appear to be transcribed and translated into a polypeptide of very unusual composition. Whereas these 2549-bp repeats are evident by Southern blotting, sequence analysis reveals a finer tandemly repetitive substructure: more than half of the 249-bp repeat length consists of tandem 24-bp subrepeats , and these in turn may have been generated from even shorter sequences. Comparisons with partial BRb and BR1 sequences reveal that this hierarchically repetitive sequence structure is typical of BR genes. It resembles the structure of some satellite sequences, suggesting that mechanisms leading to satellite DNA evolution may also operate in the evolution of structural genes.

Animals↗
PubMed1980

Periodicities and tandem repeats in a Balbiani ring gene.

The Balbiani ring (BR) DNAs show prominent periodicities of restriction enzyme sites. Studies using a cloned fragment of the BRc gene strongly suggest that these periodicities reflect the existence of tandemly repetitive sequences within BR DNA. Tandem repeats measuring 54-58 bp have been demonstrated by partial sequence analysis of the BRc clone; the restriction site periodicities suggest the existence of additional 175 (= 3 X 58) and 1050 (= 6 X 175) bp repeat units. The short, medium and long repeats (58, 175 and 1050 bp, respectively) show sequence homology. Constrained unequal crossing over (resulting from misalignment of repeat arrays, usually by one repeat) is proposed as the mechanism for evolution of short, medium and long repeats from each other, in a manner analogous to evolution of satellite DNA sequences. Paradoxically, the dominant restriction site periodicities appear to be more conservative than might be expected on the basis of the overall sequence divergence between the sequenced repeats. This may be a consequence of functionally important, long-range amino acid or oligopeptide periodicities (for example, Asp x Ser or Glu x Ser corresponding to Hinf I sites) in the BRc protein product, in conjunction with preferential use of certain synonymous codons.

Animals↗
PubMed1977

The repetition frequency of DNA in Balbiani ring 2 of Chironomus thummi.

The RNA of Balbiani ring BR2 of polytene chromosomes from Chironomus thummi salivary glands was microisolated and reassociated in the presence of an excess of total larval DNA. BR2 RNA reacts as a single component with a C0t 1/2 of 8.6. Ribosomal precursor RNA from microisolated nucleoli reassociates under identical conditions with a C0t 1/2 of 12.3. These C0t 1/2-values suggest repetition frequencies in the range of 35 and 50 for ribosomal DNA and Balbiani ring 2 DNA, respectively. The data presented here favour the view that the gene for BR2 RNA of C. thummi is internally repeated and contains only one type of DNA sequence.

Animals↗
PubMed1976

RNA, RIBOSOMAL/*BIOSYNon of ribosomal 5S RNA genes in Chironomus thummi by in situ hybridization of iodinated 5S RNA.

5 S RNA of Chironomus thummi larvae was purified from total phenol extracted RNA by gel filtration and labelled to about 10(7) dpm/mug with carrier-free iodine-125. After hybridization in situ of 125I-5 S RNA and autoradiography only region B3c-e (containing two "normal" and two very faint bands) of chromosome II of salivary gland cells was highly labelled. In chromosomes of an animal showing pairing discontinuities a clearly "heterozygous" labelling of the 5 S RNA region was found. Region B3c-e shows no clearcut morphological signs of puffing or autoradiographically detectable 3H-uridine incorportion in spite of a continuous synthesis of 5 S RNA in salivary gland cells.

Animals↗
PubMed1975

Molecular characterization of an insect genome: Chironomus thummi.

DNA extracted from Chironomus thummi larvae was studied by isopycnic centrifugation in CsCl, thermal denaturation and DNA-DNA reassociation techniques. The mean G+C content of the C. thummi DNA is 28-29% as indicated both by centrifugation in CsCl and thermal denaturation. According to optical reassociation analysis of total DNA and of isolated DNA fractions the C. thummi genome is composed of at least four components. About 80% of the DNA is classified as unique with a kinetic complexity of nearly 7 X 10(10) daltons. 6-8% intermediate DNA exhibits a kinetic complexity slightly above 10(8) daltons with a mean repetition frequency of 35. 11-13% fast-reassociating DNA has a kinetic complexity slightly above 10(6) daltons with a mean repetition frequency of 6000. 3-5% of the DNA cannot be properly studied by the optical reassociation technique and probably contains inverted repeats. The thermal denaturation behaviour of isolated DNA fractions indicated that most of the repetitive sequences in the C. thummi genome are tightly interspersed.

Animals↗
PubMed1975

The location of repeated DNA sequences in the chromosomes of Chironomus tentans.

Polytene chromosomes of Chironomus tentans were hybridized in situ with in vivo labelled nuclear and chromosomal RNA. Nuclear RNA formed hybrids preferentially in five distinct regions considered to contain clustered, repeated DNA sequences. These are the two nucleolar organizer regions, Balbiani ring 1 and 2, and the 5 S RNA genes in region 2A of chromosome II, which together comprised almost 70% of the total number of grains over the complement. The remaining grains were diffusely distributed over the chromosomes. There was a significant difference in the distribution of grains when RNA from different chromosomes was used for hybridization. Chromosome I RNA hybridized preferentially with chromosome I, and chromosome II+III RNA preferentially with chromosome II+III. Some regions within the chromosomes hybridized significantly more chromosomal RNA than other regions. A considerable cross-hybridization of RNA from one particular type of chromosome with the other chromosomes was also found. It is concluded that repeated DNA sequences which hybridize with heterogeneous chromosomal RNA in C. tentans are widely dispersed in the genome. Some of these sequences have a delimited localization, others are dispersed, and some sequences which are transcribed in one particular chromosome are present also in the other chromosomes.

Amino Acid Sequence↗
PubMedDate not supplied

Sugars as signal molecules in plant seed development.

Higher plants as sessile organisms react very flexible to environmental changes and stresses and use metabolites like glucose, sucrose and nitrate not only as nutrients but also as signals as part of their life strategies. The role of metabolites as signal molecules has attracted considerable interest during recent years. Data reviewed here for developing plant seeds suggest a trigger function of especially sugars also in development in that metabolic regulatory control can override developmental regulation, i.e., the developmental programme only continues normally if a certain metabolic state is sensed at a given time point in a given cell or tissue. Several experimental strategies have provided mainly correlative evidence that certain sugar levels and/or the resulting changes in osmotic values are necessary within defined tissues or cells to maintain a distinct stage of differentiation or to proceed with the developmental programme. In young legume seeds, but certainly also in other tissues, a high hexose (probably mainly glucose) level seems to maintain the capacity of cells to divide whereas - later in seed development - a certain sucrose level is necessary to induce storage-associated cell differentiation. A major determinant of embryo hexose levels in young legume seeds is an apoplastic invertase preferentially expressed in the inner cell layers of the seed coat. The enzyme cleaves the incoming photoassimilate sucrose into glucose and fructose. During development the tissue harbouring the invertase is degraded in a very specific spatial and temporal pattern as part of the developmental programme and is thus creating steep glucose gradients within the cotyledons. These gradients can be measured at nearly cellular resolution and were found to be correlated positively with cell division rate and negatively with cell differentiation and storage activities. A hexose and a sucrose transporter accumulating only in the epidermal cell layer of the cotyledons seem to be essential in creating and maintaining these gradients. To gain further insights into the role of metabolites, especially sugars, as triggers of developmental processes we foremost have to identify receptor molecules already characterised in yeast, and to describe and understand the signal transduction networks involved.

Glucose↗