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Membrane location of a deoxyribonuclease implicated in the genetic transformation of Diplococcus pneumoniae
Abstract:
The cellular localization of enzymes in Diplococcus pneumoniae was examined by fractionation of spheroplasts. A deoxyribonuclease implicated in the entry of deoxyribonucleic acid (DNA) into the cell during genetic transformation was located in the cell membrane. This enzyme, the major endonuclease of the cell (endonuclease I), which is necessary for the conversion of donor DNA to single strands inside the cell and oligonucleotides outside, thus could act at the cell surface. Another enzyme, the cell wall lysin (autolysin), was also found in the membrane fraction. Other enzymes, including amylomaltase, two exonucleases, and adenosine triphosphate-dependent deoxyribonuclease, and a restriction type endonuclease, were located in the cytosol within the cell. None of the enzymes examined were predominantly periplasmic in location. Spheroplasts were obtained spontaneously on incubation of pneumococcal cells in concentrated sugar solutions. The autolytic enzyme appears to be involved in this process. Cells that were physiologically competent to take up DNA formed osmotically sensitive spheroplasts two to three times faster than cells that were not in the competent state. Although some genetically incompetent mutants also formed spheroplasts more slowly, other such mutants formed them at the faster rate.
Insights
Enzymes crucial for genetic transformation in Diplococcus pneumoniae, including deoxyribonuclease, are located in the cell membrane. This finding suggests key steps in DNA uptake occur at the cell surface.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Understanding enzyme localization is crucial for elucidating cellular processes like genetic transformation.
- Diplococcus pneumoniae is a key model organism for studying bacterial genetics and DNA uptake mechanisms.
Purpose of the Study:
- To determine the cellular localization of various enzymes in Diplococcus pneumoniae.
- To investigate the role of enzyme location in the process of genetic transformation and DNA entry.
Main Methods:
- Fractionation of Diplococcus pneumoniae spheroplasts to isolate cellular components.
- Enzyme activity assays to identify and characterize enzymes within different cellular fractions.
- Correlation of enzyme localization with cellular competence for DNA uptake.
Main Results:
- A deoxyribonuclease (endonuclease I), essential for DNA processing during transformation, was localized to the cell membrane.
- The cell wall lysin (autolysin) was also found in the membrane fraction.
- Other enzymes, including amylomaltase, exonucleases, and restriction endonucleases, were located in the cytosol; no enzymes were predominantly periplasmic.
Conclusions:
- Key enzymes involved in deoxyribonucleic acid (DNA) entry and processing during genetic transformation are located at the cell membrane.
- The autolytic enzyme may play a role in spheroplast formation, which occurs faster in DNA-competent cells.
- Enzyme localization provides insights into the surface-associated nature of DNA uptake in Diplococcus pneumoniae.