GTP-binding proteins in rat liver nuclear envelopes

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Nuclear transport and nuclear envelope (NE) reassembly post-mitosis are energy-dependent processes requiring GTP and ATP.
• Understanding the proteins involved in these fundamental cellular events is key to comprehending nuclear function.

Purpose of the Study:

• To identify and localize GTP-binding proteins within the nuclear envelope.
• To investigate the presence and characteristics of ATP-binding proteins in the NE.

Main Methods:

• Combined [alpha-32P]GTP binding to Western-blotted NE proteins and UV crosslinking of [alpha-32P]GTP for protein identification.
• Utilized NE subfractionation techniques to determine protein localization.
• Performed comparative crosslinking studies with [alpha-32P]ATP.

Main Results:

• Identified five low molecular mass GTP-binding proteins (23-26 kDa) and major photolabeled GTP-binding proteins (31, 33, 47, 53, 140 kDa) in the NE.
• GTP-binding proteins preferentially localize to the inner nuclear membrane.
• Discovered distinct GTP-binding protein profiles between the NE and rough endoplasmic reticulum, with a notable 53 kDa NE protein absent in the ER.
• Identified three specific ATP-binding proteins (74, 78, 160 kDa) in the NE.

Conclusions:

• The identified GTP- and ATP-binding proteins are localized within the NE in positions suitable for roles in nuclear transport.
• These proteins likely participate in the GTP-dependent fusion of nuclear membrane vesicles during nuclear envelope reassembly.
• The findings highlight specific protein compositions of the NE distinct from other cellular compartments like the ER.