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Thymidylate synthetase during synchronous nuclear division cycle and differentiation of Physarum polycephalum
Abstract:
Thymidylate synthetase and thymidine kinase activities in wild type strain M3b and in thymidine kinase-deficient mutant TU63 of Physarum polycephalum are studied. Whenever nuclear division occurs in macroplasmodia of wild type, thymidine kinase and thymidylate synthetase activities sharply increase, although the increase of thymidylate synthetase activity is less pronounced than thymidine kinase activity. This is also true for other investigated nuclear divisions during the life cycle of P. polycephalum. It is shown for the first time that thymidylate synthetase is a periodically fluctuating enzyme during the naturally synchronous nuclear division cycle of P. polycephalum with a peak of specific activity in the S phase. In macroplasmodia, as well as after germination of microsclerotia of M3b, thymidine kinase is the dominant enzyme, whereas at the time of the precleavage mitosis in sporulating macroplasmodia thymidylate synthetase is the predominant enzyme. This study describes and compares both dTMP-synthesizing enzymes during proliferation and differentiation of the same organism.
Insights
This study reveals that thymidine kinase and thymidylate synthetase activities fluctuate with nuclear division in Physarum polycephalum. Thymidylate synthetase shows periodic activity, peaking during the S phase of the cell cycle.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Thymidylate synthetase and thymidine kinase are key enzymes in DNA synthesis.
- Understanding their regulation is crucial for comprehending cell proliferation and differentiation.
- Physarum polycephalum offers a model system with naturally synchronous nuclear division.
Purpose of the Study:
- To investigate and compare the activities of thymidylate synthetase and thymidine kinase during the cell cycle of Physarum polycephalum.
- To characterize the enzymatic profiles during proliferation and differentiation in this organism.
- To determine the temporal expression patterns of these dTMP-synthesizing enzymes.
Main Methods:
- Enzyme activity assays were performed on wild-type (M3b) and thymidine kinase-deficient mutant (TU63) strains of Physarum polycephalum.
- Enzyme activities were measured at different stages of the nuclear division cycle, including macroplasmodia and microsclerotia germination.
- Specific activity of thymidylate synthetase was analyzed in relation to the S phase of the cell cycle.
Main Results:
- Both thymidine kinase and thymidylate synthetase activities significantly increased with nuclear division in wild-type Physarum polycephalum.
- Thymidylate synthetase activity exhibited periodic fluctuations, with a peak during the S phase, a novel finding for this enzyme.
- Thymidine kinase was the dominant enzyme during macroplasmodia proliferation and microsclerotia germination, while thymidylate synthetase predominated during pre-cleavage mitosis in sporulating macroplasmodia.
Conclusions:
- Thymidylate synthetase and thymidine kinase activities are tightly regulated and linked to the nuclear division cycle in Physarum polycephalum.
- The distinct temporal expression patterns suggest specialized roles for these enzymes during different phases of proliferation and differentiation.
- This study provides a comprehensive comparison of dTMP-synthesizing enzymes in a single organism, highlighting their dynamic regulation.