RNA



Overexpression of truncated Nmd3p inhibits protein synthesis in yeast


JONATHAN P.  BELK a1, FENG  HE a1 and ALLAN  JACOBSON a1c1
a1 Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655-0122, USA

Abstract

The yeast NMD3 gene was identified in a two-hybrid screen using the nonsense-mediated mRNA decay factor, Upf1p, as bait. NMD3 was shown to encode an essential, highly conserved protein that associated principally with free 60S ribosomal subunits. Overexpression of a truncated form of Nmd3p, lacking 100 C-terminal amino acids and most of its Upf1p-interacting domain, had dominant-negative effects on both cell growth and protein synthesis and promoted the formation of polyribosome half-mers. These effects were eliminated by truncation of an additional 100 amino acids from Nmd3p. Overexpression of the nmd3[Delta]100 allele also led to increased synthesis and destabilization of some ribosomal protein mRNAs, and increased synthesis and altered processing of 35S pre-rRNA. Our data suggest that Nmd3p has a role in the formation, function, or maintenance of the 60S ribosomal subunit and may provide a link for Upf1p to 80S monosomes.

(Received January 4 1999)
(Revised March 1 1999)
(Accepted May 19 1999)


Key Words: mRNA; nonsense-mediated mRNA decay; ribosome; rRNA processing.

Correspondence:
c1 Reprint requests to: Allan Jacobson, Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, Massachusetts 01655-0122, USA; e-mail: ajacob@ummed.edu.