A New Mu Element from a Robertson’s Mutator Line
Robertson (8) described a maize line that, when self-pollinated, generated a 50-fold higher frequency of recessive mutants than expected spontaneously. Approximately 40% of these mutations were unstable genetically, a characteristic of transposon-induced mutants. The first insertional mutagen from a Robertson’s Mutator line, Mu1, was identified and cloned from an unstable mutant allele of Adh1 (3,9). Nine bp of genomic intron-1 DNA was duplicated upon insertion. A complete sequence analysis (2) of the Mu1 element determined that the 1,367-bp element contained 215-bp terminal repeats and 100-bp internal direct repeats. All Mutator lines were found to contain 10–70 copies of Mu1-homologous sequences (1,3). Zero-2 copies of Mu1 exist in non-Mutator lines (3,6). There are one larger and three smaller Mu1-related elements in Mutator lines (10). The largest-sized Mu1-family element described, Mu2 (also called Mu1.7), has a few hundred additional base pairs of internal DNA as compared to Mu1 (10).
KeywordsMutator Line Terminal Inverted Repeat Maize Line Adh1 Gene Terminal Inverted Repeat Sequence
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