Nucleocytoplasmic transport and distribution of an amino acid, in situ

Abstract

Ultra-low temperature techniques (microdissection and autoradiography) were used to study the nucleocytoplasmic distribution and transport of α-aminoisobutyric acid (AIB) in an amino acid-accumulating cell. In amphibian oocytes incubated in AIB, the nuclear concentration of this non-metabolizable amino acid exceeds the cytoplasmic concentration by 45 %, remaining constant both over time and with variation in substrate concentration. The kinetics of uptake suggest that this nucleo-cytoplasmic asymmetry arises from solubility differences between the 2 compartments, and that the nuclear envelope plays a negligible role in amino acid transport. A solute exclusion model is offered to explain the nucleocytoplasmic asymmetry.