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I2B is a small cytosolic protein that participates in vacuole fusion

P Slusarewicz1, Z Xu, K Seefeld

  • 1Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755-3844, USA.

Proceedings of the National Academy of Sciences of the United States of America
|May 27, 1997
PubMed

Insights

Two low molecular weight activities, LMA1 and LMA2, are essential for Saccharomyces cerevisiae vacuole inheritance. LMA2 is monomeric protease B inhibitor 2 (I2B), with a novel function in vacuole fusion distinct from its inhibitory role.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Yeast Genetics

Background:

  • Vacuole inheritance in Saccharomyces cerevisiae is a complex process.
  • Two low molecular weight activities, LMA1 and LMA2, have been identified as crucial for this process.
  • LMA1 is known to be a heterodimer of thioredoxin and protease B inhibitor 2 (I2B).

Purpose of the Study:

  • To elucidate the molecular identity and function of LMA2.
  • To determine the role of protease B inhibitor 2 (I2B) in vacuole fusion.
  • To differentiate the functions of LMA1 and LMA2 in vacuole inheritance.

Main Methods:

  • Biochemical characterization of LMA2.
  • Analysis of vacuole fusion in yeast strains with varying protease B activity.
  • Comparative studies of LMA1 and LMA2 activities in vacuole fusion and protease B inhibition.

Main Results:

  • LMA2 was identified as monomeric I2B.
  • The protease inhibitor activity of I2B is not directly responsible for promoting vacuole fusion.
  • LMA1, the thioredoxin-I2B complex, exhibits significantly higher activity in promoting vacuole fusion compared to monomeric I2B (LMA2).

Conclusions:

  • Monomeric I2B (LMA2) plays a distinct role in vacuole fusion, separate from its protease inhibitory function.
  • Complex formation of I2B with thioredoxin (LMA1) enhances its role in vacuole fusion.
  • These findings establish a new function for I2B in Saccharomyces cerevisiae vacuole inheritance.

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