idl-B mutants lack TRp protein. (A) Representative immunoblots of wild-type (wt), idl-B alleles, trp alleles, idl-B heterozygotes and trans-heterozygous idl-B/trp flies. TRp protein was absent from all homozygous trp and idl-B alleles. The two idl-B alleles failed to complement with trp as depicted by the lack of TRp protein in the trans-heterozygous idl-B/trp samples. INAD and Rh1, in contrast, were present in all fly stocks. All samples contained 10 heads from darkraised flies. (B) Representative cross-sections of single ommatidia from dark-raised wild-type, idl-B1/trp343, and idl-B2/trp343 flies immunostained for INAD. Note that INAD is mislocalized in both idl-B1/trp343 and idl-B2/trp343, indicating that both idl-B alleles failed to complement with trp for INAD localization. phase-contrast images are shown to illustrate the wild-type structure of all three genotypes analyzed.