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Identification of casein kinase II and phosphorylated proteins associated with messenger ribonucleoproteins particles
Abstract:
Messenger ribonucleoprotein (mRNP) particles, isolated from reticulocyte polysomes and purified by buoyant density centrifugation in metrizamide, contained an endogenous protein kinase activity. The cyclic-nucleotide-independent protein kinase phosphorylated casein using either ATP or GTP as the phosphoryl donor and had properties similar to casein kinase II, an enzyme previously purified and characterized from the post-ribosomal supernate of reticulocytes. Antibody prepared to casein kinase II was shown to inhibit the protein kinase activity in the mRNP particles. The endogenous enzyme phosphorylated four peptides (Mr 125 000, 107 000, 76 000 and 63 000) in the mRNP particle. Three of the four peptides, plus another (Mr 175 000), were phosphorylated by purified casein kinase II while two peptides (Mr 95 000 and Mr 76 000) were phosphorylated with casein kinase I. The mRNP particles were not substrates for the cAMP-dependent protein kinases.
Insights
Messenger ribonucleoprotein (mRNP) particles possess a protein kinase activity similar to casein kinase II. This endogenous enzyme phosphorylates specific peptides within mRNP particles, suggesting a role in protein regulation.
Area of Science:
- Molecular Biology
- Biochemistry
- Cell Biology
Background:
- Messenger ribonucleoprotein (mRNP) particles are crucial for mRNA transport and translation.
- Protein phosphorylation plays a vital role in regulating cellular processes.
Purpose of the Study:
- To characterize the protein kinase activity present in reticulocyte mRNP particles.
- To identify the substrates of this endogenous kinase and compare it with known casein kinases.
Main Methods:
- Isolation and purification of mRNP particles from reticulocyte polysomes using metrizamide density centrifugation.
- Assay of endogenous protein kinase activity using ATP or GTP.
- Phosphorylation of casein and mRNP-associated peptides.
- Inhibition studies using antibodies against casein kinase II.
Main Results:
- mRNP particles contain a cyclic-nucleotide-independent protein kinase activity resembling casein kinase II.
- This endogenous kinase phosphorylates four specific peptides within the mRNP particle.
- Purified casein kinase II phosphorylates three of these peptides, while casein kinase I phosphorylates two others.
- Antibodies to casein kinase II inhibit the mRNP-associated kinase activity.
Conclusions:
- Reticulocyte mRNP particles possess an intrinsic casein kinase II-like activity.
- This kinase likely phosphorylates specific mRNP proteins, potentially regulating mRNA metabolism.
- The findings highlight the importance of post-translational modifications within mRNP particles.