Conserved nuclear export sequences in Schizosaccharomyces pombe Mex67 and human TAP function in mRNA export by direct...

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Mex67 is a homolog of human TAP, a key mRNA export factor.
• In Schizosaccharomyces pombe (S. pombe), Mex67 is not essential for mRNA export.
• S. pombe also encodes a homolog of the TAP cofactor, p15, which is also not essential for mRNA export.

Purpose of the Study:

• To identify and characterize novel nuclear export signals within Mex67.
• To investigate the functional conservation of these signals in human TAP.
• To explore the role of these signals in mediating mRNA export and their interaction with nucleoporins.

Main Methods:

• Identification and characterization of nuclear export signals (NES I and NES II) in Mex67.
• In vitro binding assays with FG-containing sequences of S. pombe Nup159 and Nup98.
• Functional assays in S. pombe and HeLa cells to assess nuclear export activity.
• Complementation assays in a synthetic lethal S. pombe strain to evaluate function in the absence of p15.

Main Results:

• Two distinct nuclear export signals, NES I and NES II, were identified in Mex67 (amino acids 434-509).
• These NESs are functionally conserved in human TAP and directly bind to FG-nucleoporins (Nup159, Nup98).
• Mutants lacking NES I or NES II binding to FG-nucleoporins failed to mediate nuclear export, and these NESs could rescue mRNA export defects in the absence of p15.

Conclusions:

• Mex67 and TAP possess novel nuclear export signals that interact with FG-nucleoporins.
• These NESs provide alternative pathways for Mex67/TAP delivery to the nuclear pore complex.
• The identified NESs are functionally conserved and can operate independently of the p15 cofactor, offering new insights into mRNA export mechanisms.