Mutations in the three predicted furin cleavage sites: amino acid replacement R325A within the "Main" high probability site, amino acid replacement K334N within the "Shadow" low probability site and amino acid replacement R126A within the "Pro" predicted site.
gbb4 homozygotes show complete lethality in the presence of one copy of gbbR126A.R325A.K334N.T:Zzzz\FLAG.
gbbR126A.R325A.K334N.Tag:FLAG fails to rescue gbbD20/Df(2R)bw-S46