Analysis of nonstop mRNA decay in Caenorhabditis elegans

Nonstop mRNA decay (NSD) is an mRNA surveillance mechanism in S. cerevisiae and mammalian cells that selectively degrades mRNAs lacking stop codons. I constructed an in vivo transgenic GFP reporter system to test whether NSD exists in C. elegans and to identify components of NSD using a genetic screen. The screen identified multiple independent intragenic revertants of the GFP reporter gene, but no extragenic suppressor mutations. I used the revertant alleles to demonstrate unequivocally that NSD exists in C. elegans. I tested candidate genes known to be involved in mRNA degradation in yeast and mammalian cells and observed that, as in S. cerevisiae, RNAi targeting certain components of the 3' to 5' decay pathway appear to reduce the efficiency of C. elegans NSD. RNAi targeting certain components of the 5' to 3' decay pathway also appeared to reduce the efficiency of NSD.; While investigating the reasons that the original genetic screen did not identify extragenic suppressor mutations involved in the NSD pathway, I observed that stretches of adenosines 27 nucleotides or longer within an open reading frame reduce protein expression without affecting mRNA abundance. It is presently unknown whether this effect reflects translational efficiency of oligo(A)-containing mRNAs or instability of the resulting polypeptides. My results demonstrate that NSD is conserved in nematodes and indicate that mRNAs lacking stop codons are regulated at the level of mRNA abundance and by translational and/or post-translational mechanisms.