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Results for “light strand promoter”

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PubMed2022

The human mitochondrial genome contains a second light strand promoter.

The human mitochondrial genome must be replicated and expressed in a timely manner to maintain energy metabolism and supply cells with adequate levels of adenosine triphosphate. Central to this process is the idea that replication primers and gene products both arise via transcription from a single light strand promoter (LSP) such that primer formation can influence gene expression, with no consensus as to how this is regulated. Here, we report the discovery of a second light strand promoter (LSP2) in humans, with features characteristic of a bona fide mitochondrial promoter. We propose that the position of LSP2 on the mitochondrial genome allows replication and gene expression to be orchestrated from two distinct sites, which expands our long-held understanding of mitochondrial gene expression in humans.

Adenosine Triphosphate↗

PubMed1978

Fibrinogen-fibrin transformations characterized during the course of reaction by their intermediate structures. A light scattering study in dilute solution under physiological conditions.

Intermediate structures of human fibrin formed under physiological conditions were investigated by means of light scattering in the course of the polymer/network formation. Very low fibrinogen concentrations (c = 0.03--0.13 mg/ml) were used to lower the polymerization rate, and thrombin at five concentrations (0.0085--0.04 N.I.H./ml) was used for initiation. The light scattering data were evaluated from (i) a Zimm plot, (ii) a Holtzer plot, i.e., hRtheta/Kc vs. h2, and (iii) a Kratky plot, i.e., h2Rtheta/KC vs. h2. In the beginning of the polymerization process rod-like structures are formed. The dimensions of the rod-like monomeric unit in the fibrin polymer are 112 X 3.9 nm and agree with the dimensions of fibrinogen, which also was found to be a thin rod of 105 +/- 10 nm length and 3.9 nm diameter. The mass per unit length, obtained from the asymptote in the Holtzer plot, initially increases only slightly but for high thrombin concentrations increases steeply when a critical length of 1000 nm is exceeded. At this point also the total scattering behaviour changes considerably. The upturn in the Zimm plot and the occurrence of a maximum in the Kratky plot are clear indications for the onset of branching. At low thrombin concentrations the kink in the curve of Mw/Lw against Mw becomes smoothed out because of nonspecific side-by-side aggregation of fibrin strands. The results are discussed and compared with earlier findings by others, and lead to the following conclusions. (i) Fibrinogen is a polymer with some flexibility and can exist in conformations of a stretched rod 105 nm in length, a folded rod of 45 nm in length, and a banana-like conformation of 94 nm circumference. (ii) Under the conditions of the present work, fibrinogen has the thin stretched rod conformation, and has the same dimensions as the repeating unit in the fibrin polymer. (iii) After approx. 10--12 units, end-to-end aggregated monomer branching occurs. (iv) The end-to-end aggregation is promoted by the cleavage of A peptides, branching is caused by the cleavage of B peptides while side-by-side aggregation of strands is caused by nonspecific van der Waals interaction.

Fibrin↗

PubMed1976

Content and expression of integrated viral DNA in hamster cells transformed by nondefective adenovirus type 2- simian virus 40 hybrid viruses.

Hamster cells transformed by adenovirus 2 (Ad2) and five nondefective Ad2-simian virus 40 (SV40) hybrid viruses are all of the Ad2-transformed phenotype. All lines accumulate Ad2 RNA and Ad2 T antigen; two hybrid-transformed lines accumulate SV40 RNA, but only one contains detectable amounts of SV40 antigens. We examines selected lines from this group of transformed hamster cells for Ad2 DNA content and viral RNA expression by using hydroxyapatite chromatography and separated strands of labeled viral DNA as probes. All lines studies contain 1 to 2 Ad2 genome equivalents per haploid equivalent of cell DNA. The expression of Ad2 RNA exhibits two distinct patterns. In one pattern, transcription of the heavy strand of Ad2 DNA is less than that of the light strand, whereas in the second pattern of Ad2 RNA expression the extent of heavy-strand transcription is greatly increased. In the two lines containing SV40 RNA, the entire SV40 (-) strand is transcribed; the (+) strand is not expressed in these cells. These patterns of viral RNA expression suggest the possibility that host promoters may play a role in regulating transcription of integrated viral DNA.

Adenoviridae↗

PubMed2024

DciA, the Bacterial Replicative Helicase Loader, Promotes LLPS in the Presence of ssDNA.

The loading of the bacterial replicative helicase DnaB is an essential step for genome replication and depends on the assistance of accessory proteins. Several of these proteins have been identified across the bacterial phyla. DciA is the most common loading protein in bacteria, yet the one whose mechanism is the least understood. We have previously shown that DciA from Vibrio cholerae is composed of a globular domain followed by an unfolded extension and demonstrated its strong affinity for DNA. Here, we characterize the condensates formed by VcDciA upon interaction with a short single-stranded DNA substrate. We demonstrate the fluidity of these condensates using light microscopy and address their network organization through electron microscopy, thereby bridging events to conclude on a liquid-liquid phase separation behavior. Additionally, we observe the recruitment of DnaB in the droplets, concomitant with the release of DciA. We show that the well-known helicase loader DnaC from Escherichia coli is also competent to form these phase-separated condensates in the presence of ssDNA. Our phenomenological data are still preliminary as regards the existence of these condensates in vivo, but open the way for exploring the potential involvement of DciA in the formation of non-membrane compartments within the bacterium to facilitate the assembly of replication players on chromosomal DNA.

DNA, Single-Stranded↗

PubMed1977

Some morphological aspects of the synaptonemal complex in higher plants.

The synaptonemal complex is illustrated in electron micrographs from pollen mother cells (p.m.cs) of the following plants: Fritillaria lanceolata, Allium fistulosum, Tulbaghia violacea, Luzula purpurea, Phaedranassa viridiflora and the tulip cultivar Keiserkroon. The possibility that the lateral elements in synaptonemal complexes of plants are tubiform structures is discussed in relation to their fine structure and in the light of a deformity seen in them. An assessment of the evidence suggesting that both lateral and central elements in the complex are ribonucleoprotein structures is made. The effect of brief water treatment on the chromatin and synaptonemal complex at zygotene in p.m.cs of the Phaedranassa is discussed, particularly with reference to two precisely oriented axial strands then seen running between the lateral elements. Examination of stages of premeiotic interphase and early leptotene in p.m.cs of the Fritillaria, revealed that the axial cores laid down at leptotene are formed first in heterochromatic regions, which in this species are locked in chromocentres that persist until pachytene. Further, at leptotene the chromatin in these parts was singularly more decondensed (diffuse) than at any other period, including the premeiotic interphase, subsequent stages of meiosis and mitotic cycle in meristems. It is suggested that the diffuse state of the chromatin in chromocentres at the onset of leptotene, allows the necessary freedom of movement required to promote homologous pairing of the heterochromatic segments. Evidence of such a movement was indicated by a change in position of the nucleoli, which moved from a more central position at early premeiotic interphase to a peripheral one at the onset of leptotene, when they are seen adpressed to the nuclear envelope.

Cell Nucleus↗