--Peter A. Peterson
A number of derivatives of the a-m(Au) allele are non-responsive to En colorless or pale types. Some, however, are responsive to En. They are similar to the a-m-15719 that was described by McClintock that is colored in the absence of En/Spm but is suppressed with En/Spm and shows mutability. The a-m-15719 allele is in the second exon of the A1 gene and the explanation for the coloration of the A1 gene with the I insert was based on the position of the insert--namely in the last and next to the last nucleotide (3') of the second exon. Appropriately located splice sites splice out the insert. The a-m(Au)pale-m(r) derivatives are at position 336 into the second exon with an orientation the same as that of the A1 gene promoter. Thus, there must exist similar splice sites in this region of the second exon.
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