Poly(A) polymerase phosphorylation is dependent on novel interactions with cyclins

Area of Science:

• Molecular Biology
• Cell Cycle Regulation
• Enzymology

Background:

• Poly(A) polymerase (PAP) is known to be negatively regulated by cyclin B-cdc2 kinase hyperphosphorylation during M phase.
• Cyclin recognition motif (CRM) sequences typically mediate interactions with G(1)-phase cyclins in cell cycle regulators.

Purpose of the Study:

• To investigate the direct interaction between poly(A) polymerase (PAP) and cyclin B(1).
• To characterize the role of a novel cyclin recognition motif (CRM) in PAP's interaction with different cyclin types and its functional consequences.

Main Methods:

• Direct binding assays to confirm PAP-cyclin B(1) interaction.
• Analysis of PAP's amino acid sequence for homology to cyclin recognition motifs (CRM).
• In vitro kinase assays using cyclin-cdk pairs and PAP, including experiments with CRM peptides at varying concentrations.

Main Results:

• Direct binding between PAP and cyclin B(1) was demonstrated, mediated by a CRM in PAP.
• PAP's CRM interacts with both G(1)- and G(2)-type cyclins and is a substrate for phosphorylation by cyclin-cdk pairs.
• PAP's CRM peptide exhibits concentration-dependent effects: high concentrations inhibit binding and phosphorylation, while low concentrations stimulate these activities.

Conclusions:

• Poly(A) polymerase (PAP) is directly regulated by cyclin-dependent kinases throughout the cell cycle.
• A novel type of CRM in PAP functionally interacts with both G(1)- and G(2)-type cyclins in a concentration-dependent manner, revealing a new regulatory mechanism.