Molecular identification of smg-4, required for mRNA surveillance in C. elegans

Premature termination codons trigger a process in eukaryotes known as nonse nse mediated decay or mRNA surveillance, resulting in the rapid decay of th e aberrant transcript. Studies in C. elegans have shown this system is medi ated by seven smg genes and can prevent the accumulation of toxic, truncate d peptides. Here we report the cloning of smg-4 by physical mapping and fun ctional rescue assays. The minimal rescuing activity is found within a geno mic operon, encoding a novel protein. The final exon of the gene is alterna tively spliced for expression of two different isoforms. Although no known genes were found to exhibit significant homology to smg-4, a novel conserve d domain has been identified by alignment with sequences defined by express ed sequence tags (ESTs) from a variety of organisms. Furthermore, we descri be a homolog from C, briggsae, which will rescue C. elegans smg-4 mutants. The C. elegans gene has been fused to green fluorescent protein (GFP). This SMG4:GFP fusion exhibits nuclear accumulation and diffuse cytoplasmic stai ning, and further localizes to what appear to be perinuclear and cytoplasmi c punctate structures. (C) 2001 Elsevier Science B.V. All rights reserved.