DNA insertion in the first intron of maize Adh1 affects message levels: cloning of progenitor and mutant Adh1 alleles.

A genetically unstable mutant allele of maize alcohol dehydrogenase-1 (Adh1) causes reduced levels of messenger RNA. This mutant was derived from a Robertson's mutator genetic background and previously was shown to be associated with an approximately 1.5-kilobase insertion. This report compares a genomic clone of the allele, Adh1-S3034, with a clone of its progenitor nonmutant allele, Adh1-S. No rearrangements of either recombinant molecule occurred during the cloning process. The mutant differs from its progenitor allele by the insertion of 1.4 kilobases of new DNA. Sequence determination of the insertion borders localized it to intron-1, 73 base pairs downstream from the 5' exon/intron junction in the Adh1-S gene. Insertion of the 1.4-kilobase element was associated with a 9-base-pair direct duplication of intron sequence. We suspect that this insertion, Mu1, affects message levels by depressing RNA processing or transcription.