What do smg genes do?
The normal function of the smg genes is to promote nonsense-mediated decay (NMD) of mRNAs with premature (mutant) stop codons. In a smg- background, these mRNAs which are usually targeted for degradation stick around. If they are actually functional, but are usually (in a smg+ background) degraded and thus null, then these short but wt proteins can “suppress” (really, rescue) the mutant phenotype.