Why do some recessive mutations become dominant when in a smg- background?
Sometimes the short mutant proteins are not wt (as above), but are in fact interfering (antimorphic). In a smg+ background, these mutant mRNAs are targeted for degradation, so a homozygous mutant is like a null mutant (no mRNA translated) and a heterozygote has only the one functional copy translated into mRNA. When NMD is gone (smg- background), the mutant RNAs are translated and can dominantly interfere with wt protein function (antimorphic allele).
