A late truncation in MLE (for 'maleless', RNA helicase) produces a modifier phenotype. (a) The MLE protein contains two double stranded RNA binding motifs at the N-terminus and a large helicase domain in the middle. The C-terminus has 12 imperfect copies of a glycine-rich heptad repeat, each of which has 1 aromatic residue. The modifier allele has a 1-bp deletion in the I926 codon. The MLE21Δgly transgene carries a deletion of the heptad repeats on a genomic clone expressed from its native promoter. (b) Male and female homozygous for [w+ GMroX1-75C] who are either mle+/CyO (top) or mleI926Z/CyO (bottom). (c) The MLE21Δgly transgene rescues male viability, but not fertility. y w; mle1/CyO y+; [w+ MLE21Δgly]/+ males and females were mated and the homozygous mle1/mle1 progeny were counted and scored for eye colour and sex. The MLE21Δgly construct could not be assayed for its effect on mosaic eyes of GMroX1-75C because of the linked w+ marker.