Evidence for polyphosphate in phosphorylated nonhistone nuclear proteins

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Eukaryotic nuclear proteins are known to bind phosphates.
• The precise nature and function of these phosphate modifications are not fully understood.

Purpose of the Study:

• To investigate the structure and identity of polymeric phosphates bound to nonhistone nuclear proteins (NHPs).
• To explore the potential functional implications of polyphosphorylated NHPs in gene regulation.

Main Methods:

• Isolation and analysis of 32P-labeled and unlabeled nonhistone nuclear proteins (NHPs) from rat liver nuclei.
• Protease-trypsin digestion and alkaline beta-elimination to characterize phosphorylated fragments.
• Two-dimensional chromatography and hydrolysis to determine polyphosphate chain length and identity.

Main Results:

• Six homogeneous, phosphorylated NHP fragments with high phosphate/amino acid ratios were identified.
• Polymeric phosphates, identified as polyphosphate with chain lengths from 2 to over 200, were released.
• Evidence suggests the formation of polyphosphorylated NHPs through multiple phosphoanhydride linkages.

Conclusions:

• Nonhistone nuclear proteins (NHPs) can be polyphosphorylated, forming extensive polyphosphate chains.
• These findings suggest a potential regulatory role for polyphosphorylated NHPs in gene expression, building on known effects of free polyphosphate.