HTT and juvenile Huntington disease: Htt with a polyQ stretch containing 103 glutamine residues (Htt103Q) fused to the green fluorescent protein (GFP) is frequently used to model Huntington disease in S. cerevisiae, because the aggregation-prone Htt103Q sequence strongly inhibits yeast growth thus mimicking toxicity, while GFP allows easy microscopic monitoring of Htt103Q-GFP aggregates.