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Nucleolin (C23), a physiological substrate for casein kinase II
1Institut für Humangenetik, Universität des Saarlandes, Homburg, FRG.
Biochemical and Biophysical Research Communications
|November 15, 1988
Summary
Nucleolin, a key nucleolar phosphoprotein, is a physiological substrate for casein kinase II (CKII). Researchers confirmed this by comparing phosphopeptide patterns, demonstrating CKII
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Nucleolin (C23) is a 110 kDa phosphoprotein primarily located in the nucleolus.
- Casein kinase II (CKII) is an enzyme involved in various cellular processes.
Purpose of the Study:
- To investigate whether nucleolin is a physiological substrate for casein kinase II (CKII).
- To characterize the phosphorylation of nucleolin by CKII.
Main Methods:
- Immunodetection using an anti-nucleolin antibody.
- Phosphorylation of isolated nucleolin by purified CKII.
- Analysis of phosphopeptide patterns using partial tryptic digest.
- In vivo phosphorylation of nucleolin in tumor cells using [32P]-o-phosphate.
Main Results:
- Phosphopeptide patterns of in vitro CKII-phosphorylated nucleolin were identical to in vivo phosphorylated nucleolin from tumor cells.
- Partial tryptic digestion yielded nine distinct phosphopeptides.
- Nucleolin isolated from Krebs II mouse ascites cells incorporated approximately two moles of phosphate per mole of nucleolin when treated with purified CKII.
Conclusions:
- Nucleolin is confirmed as a physiological substrate for casein kinase II (CKII).
- The phosphorylation sites and patterns are conserved between in vitro and in vivo conditions.
- This study elucidates a key post-translational modification of nucleolin by CKII.