CHARACTERIZATION OF THE MOLECULAR DEFECT IN A NULL ALLELE OF THE OPAQUE-2 LOCUS OF MAIZE

The molecular defect in an opaque-2 (o2) mutant, previously characteri zed as a null allele, has been identified as containing an insertion o f the transposable element of the Bergamo (Bg) family. Restriction map ping and partial sequence analysis of the Bg in the o2 null allele ind icates that this element is distinct from the previously described Bg as well as the defective Bg (rbg) of the o2m(r) allele. It is, however , inserted at the same site in O2 as the rbg of o2m(r) and can transpo se when Bg is present. This study shows that, depending on genetic bac kground, this allele may not behave as a stable null which could drama tically influence the conclusions drawn from experiments based on this particular mutant.