From: ncbi-seminar-admin@ncbi.nlm.nih.gov on behalf of Landsman, David
(NLM) [landsman@mail.nih.gov]
Sent: Friday, June 07, 2002 1:43 PM
To: 'ncbi-seminar@ncbi.nlm.nih.gov'
Subject: SEMINAR: Tuesday June 24th 11am in Natcher Conference Room
ConfN6S

Hi 
Qinghu Ren from the Department of Biology at University of Rochester, New York will be presenting a seminar at the 11:00am on June 24th in Natcher Conference Room ConfN6S (6th floor). All welcome. David Landsman

Title: Essential and Non-Essential Function of Acetylation of Histone H2A and H2A.Z in Tetrahymena thermophila

Abstract:
Post-translational modifications of histones and incorporation of histone variants into nucleosomes are conserved mechanisms that likely modulate chromatin structure and function. Three forms of histone H2A exist in
Tetrahymena: major histones H2A.1, H2A.2, which make up ~80% of the total H2A, and a variant histone H2A.Z. Histone H2A.Z is highly conserved and structurally and functionally distinct from the major H2As. To better understand the in vivo function of histone acetylation in general, and of H2A.Z variant and major histone H2A acetylation in particular, we performed an in vivo mutagenic analyses of the acetylation sites in the N-terminal tails of Tetrahymena macronuclear H2A.Z or H2A. Tetrahymena cannot survive if arginines replace lysines at all six sites on the H2A.Z N-terminus. However, retention of a single acetylatable lysine is sufficient to provide the essential function of H2A.Z acetylation. The essential function of H2A.Z acetylation can be mimicked by deleting the region encompassing all six sites, or by mutations that reduce the positive charge of the N-terminus at the acetylation sites themselves, or at other sites in the tail. These properties argue that the essential function of H2A.Z acetylation is to modify a charge patch by reducing the charge of the tail. Unlike H2A.Z acetylation, neither post-translational nor co-translational acetylation of major histone H2A is essential. Tetrahymena survived with all five acetylatable lysines on the H2A N-terminus replaced by arginines, plus a mutation which abolished acetylation of the N-terminal serine normally found in the wild-type protein. We also found that the N-terminus of H2A can replace the function of the H2A.Z N-terminus, the acetylation of which is essential, indicating that the non-essential H2A acetylation can provide the essential function of H2A.Z acetylation. Surprisingly, H2A.Z(H2A.1)N chimeric protein still exhibits an essential charge patch property. Tetrahymena cells can survive with eight positive charges in the tail of the chimeric protein but not with nine.