QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

Vol. 16, Issue 9, 4046-4060, September 2005

This Article Full Text Full Text (PDF) All Versions of this Article: E05-01-0028v1 16/9/4046    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Cowan, A. T. Articles by Turkewitz, A. P. Search for Related Content PubMed PubMed Citation Articles by Cowan, A. T. Articles by Turkewitz, A. P.

Genetic, Genomic, and Functional Analysis of the Granule Lattice Proteins in Tetrahymena Secretory Granules

Andrew T. Cowan ^* , Grant R. Bowman ^* , Kyle F. Edwards ^*, J. J. Emerson , and Aaron P. Turkewitz ^*

^* Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637; Department of Ecology and Evolution, The University of Chicago, Chicago, IL 60637

Submitted January 18, 2005; Revised April 27, 2005; Accepted June 3, 2005
Monitoring Editor: Randy Schekman

In some cells, the polypeptides stored in dense core secretory granules condense as ordered arrays. In ciliates such as Tetrahymena thermophila, the resulting crystals function as projectiles, expanding upon exocytosis. Isolation of granule contents previously defined five Granule lattice (Grl) proteins as abundant core constituents, whereas a functional screen identified a sixth family member. We have now expanded this screen to identify the nonredundant components required for projectile assembly. The results, further supported by gene disruption experiments, indicate that six Grl proteins define the core structure. Both in vivo and in vitro data indicate that core assembly begins in the endoplasmic reticulum with formation of specific hetero-oligomeric Grl proprotein complexes. Four additional GRL-like genes were found in the T. thermophila genome. Grl2p and Grl6p are targeted to granules, but the transcripts are present at low levels and neither is essential for core assembly. The GRL6 cells nonetheless showed a subtle change in granule morphology and a marked reduction in granule accumulation. Epistasis analysis suggests this results from accelerated loss of GRL6 granules, rather than from decreased synthesis. Our results not only provide insight into the organization of Grl-based granule cores but also imply that the functions of Grl proteins extend beyond core assembly.

These authors contributed equally to this work.

Address correspondence to: Aaron P. Turkewitz (apturkew{at}midway.uchicago.edu).