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Phosphorylation alters the affinity of high mobility group protein HMG 14 for single-stranded DNA
Abstract:
The effect of phosphorylation on the affinity of HMG 14 from calf thymus for single-stranded DNA (ssDNA) was studied, using a cyclic GMP-dependent protein kinase from bovine lung and a nuclear protein kinase II from rat liver. When phosphorylated by G-kinase, HMG 14 eluted at 0.27 M NaCl from the ssDNA-column, whereas the native protein eluted at 0.30 M salt concentration. In contrast, phosphorylation by nuclear protein kinase II did not alter dissociation of HMG 14 from ssDNA and the phosphoprotein consequently coeluted with the native HMG 14. Thus, addition of a negative charge by phosphorylation of the Ser-6 residue by G-kinase presumably weakens the interaction between the DNA-binding amino acids of HMG 14 and the negatively charged phosphate groups of DNA.
Insights
Phosphorylation of HMG 14 protein by G-kinase reduces its affinity for single-stranded DNA (ssDNA). However, phosphorylation by nuclear protein kinase II has no effect on HMG 14 binding to ssDNA.
Area of Science:
- Biochemistry
- Molecular Biology
- Genetics
Background:
- High-mobility group (HMG) proteins are involved in DNA binding and chromatin structure.
- Phosphorylation is a key post-translational modification that can alter protein function.
- HMG 14 is a specific HMG protein known to interact with DNA.
Purpose of the Study:
- To investigate the effect of phosphorylation on the DNA-binding affinity of HMG 14.
- To compare the impact of different kinases on HMG 14 phosphorylation and DNA interaction.
Main Methods:
- Purification of HMG 14 from calf thymus.
- In vitro phosphorylation of HMG 14 using cyclic GMP-dependent protein kinase (G-kinase) and nuclear protein kinase II.
- DNA-binding assays using ssDNA-cellulose chromatography.
Main Results:
- Phosphorylation of HMG 14 by G-kinase decreased its affinity for ssDNA, causing it to elute at a lower salt concentration (0.27 M NaCl) compared to native HMG 14 (0.30 M NaCl).
- Phosphorylation of HMG 14 by nuclear protein kinase II did not alter its dissociation from ssDNA.
- The observed effect of G-kinase was attributed to the addition of a negative charge at the Ser-6 residue, weakening DNA-protein interactions.
Conclusions:
- The affinity of HMG 14 for ssDNA is modulated by specific phosphorylation events.
- G-kinase-mediated phosphorylation, but not nuclear protein kinase II-mediated phosphorylation, reduces HMG 14's binding to ssDNA.
- This suggests a regulatory mechanism where phosphorylation controls HMG 14's interaction with DNA, potentially influencing chromatin dynamics.