Insertion of an unstable element in maize Adhl affects transcription bu

Three independently isolated and unstable mutants of the maize alcohol dehydrogenase 1 gene (Adhl) have arisen by insertion of the Mu transposing element into the first intervening sequence of the progenitor Adhl allele. The mu- tants have been selected for their decreased levels of alcohol dehydrogenase 1 activity. The original mutants were unstable, giving rise to both revertant alleles and altered mutant alleles. From one of the original mutants, two derivative mutants have been recovered and described. We analyzed the effect of Mu insertion in all five of these mutants by measuring relative levels of run-off transcripts from the progenitor and mutant alleles and by comparing levels of run-off transcripts corresponding to regions lying 5' and 3' to the insertion sites. In this paper we present evidence that early transcriptional events are affected, but that, in spite of the inclusion of a 1.4-kilobase transposing