Functional histone antibody fragments traverse the nuclear envelope

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Nuclear translocation is crucial for protein function.
• Understanding the mechanisms of protein transport across the nuclear envelope is essential for cell biology.
• Specific signals or properties may dictate nuclear import and accumulation.

Purpose of the Study:

• To investigate the factors governing protein translocation across the nuclear membrane.
• To determine the role of molecular size and nuclear binding sites in protein nuclear accumulation.
• To explore the utility of microinjected antibody fragments for studying nuclear components.

Main Methods:

• Microinjection of fluoresceinated nonimmune and anti-histone IgG and F(ab)2 fragments into human fibroblast nuclei and cytoplasm.
• Observation of protein distribution within cells using fluorescence microscopy.
• Assessment of uridine incorporation to measure nuclear function inhibition.

Main Results:

• Intact IgG remained localized at the injection site, while nonimmune F(ab)2 distributed uniformly.
• Antihistone F(ab)2 fragments successfully translocated into the nucleus and accumulated there.
• Nuclear accumulation of antihistone F(ab)2 led to inhibition of uridine incorporation.

Conclusions:

• Proteins smaller than 55A with nuclear binding sites can translocate and accumulate in the nucleus without specific signal sequences.
• The 'quasibifunctional binding sites' model supports nuclear protein accumulation.
• Microinjected active F(ab)2 fragments are viable tools for investigating nuclear component location and function in living cells.