S phase-specific synthesis of dihydrofolate reductase in Chinese hamster ovary cells.
AUTOR(ES)
Mariani, B D
RESUMO
We investigated the cell cycle modulation of dihydrofolate reductase (DHFR; tetrahydrofolate dehydrogenase, 7,8-dihydroxyfolate:NADP+ oxidoreductase, EC 1.5.1.3) levels in methotrexate-resistant Chinese hamster ovary cells synchronized by mitotic selection. DNA content and DHFR concentration were analyzed throughout the cell cycle by standard biochemical techniques and by double fluorescence staining utilizing the fluorescence-activated cell sorter. We found an S phase-specific period of DHFR biosynthetic activity. Commencing within hour 2 of S phase and continuing throughout the duration of S phase, there is a 90% increase in DHFR specific activity. This results from an approximately 2.5-fold increase in the level of DHFR, while total soluble protein increases 50% during the same period. This increase is the result of new synthesis of DHFR molecules initiated after the cell is physiologically committed to DNA replication. This increase in DHFR activity through S phage parallels the increasing rate of [3H]thymidine incorporation during the same interval. The maximum peak of DHFR activity is coincident with the maximum rate of DNA synthesis, both activities occurring during the bulk of DNA replication within the last stages of the 6.5-hr S phase.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=320316Documentos Relacionados
- Structure of the dihydrofolate reductase gene in Chinese hamster ovary cells.
- Spontaneous splicing mutations at the dihydrofolate reductase locus in Chinese hamster ovary cells.
- Overproduction of dihydrofolate reductase and gene amplification in methotrexate-resistant Chinese hamster ovary cells.
- G2 phase-specific proteins of HeLa cells.
- Transient hypoxia enhances the frequency of dihydrofolate reductase gene amplification in Chinese hamster ovary cells.