| Abstract: | The Mutator transposable element system (Mu) of maize has been responsible for the induction of numerous mutable aleurone mutants of maize. Unlike similar mutants induced by other transposable element systems, the mutability of Mu-induced mutants did not seem initially to be regulated by an independent autonomous or regulator element. However, in a continuing study of two Mu-induced a1 mutable mutants (a1-Mum2) and a1-Mum3, lines have been obtained that give evidence of an independently segregating regulator of somatic mutability. Data from several generations of crossing are presented indicating that intense somatic mutability in many of these stocks is under the control of an independent regulator. However, testing of other lines, which initially gave evidence of the presence of an independent regulator, were negative. Some of these latter lines could be expected to have Mutator elements that were modified (methylated) at sites recognized by certain restriction endonucleases. Modification of Mu elements, which is known to affect the expression of somatic mutability, might, at times, be responsible for producing conditions that mimic the segregation of an independent regulator. Lines with stable derivatives of the a1-Mum2 and a1-Mum3 can recover intense somatic mutability by crossing with germinally active Mutator stocks. Thus, active Mutator lines contain regulator elements and evidence is presented suggesting that such lines have multiple copies of these elements. Most a1- Mum2 and a1-Mum3 stocks segregating for a regulator do not have germinal Mutator activity. Thus the presence of one or a few putative regulator elements does not necessarily account for the high level of germinal activity in most Mutator stocks. |
