In the En controlling element system, two readily observable functions can be ascribed to the En transposon. These include both suppressor (S) and mutator (M) functions. The assorted activities and changes associated with En can be tested by the use of an unstable "A" state, a-m(Au), phenotypically indistinguishable from standard A except for large colorless areas (A to a) in the aleurone layer. Two observations indicate that a potentially active En is associated with a-m(Au): (1) fully active En elements containing S and M are coincident isolates with changes of a-m(Au) to a-m(nr) (colorless forms) and (2) a-m(Au) responds to an independently segregating En.

By combining a-m(Au) with various colored (pale to dark) responding alleles such as a-m-1 changes that occur in the change from a-m(Au) to a-m(nr) (the colorless areas of the "A" state) can be monitored. These observations show that the En at the a-m(Au) allele expresses sm, Sm, sM and SM phenotypes (s, m indicating lack of suppressor and mutator functions, respectively). Further, the changes are not permanent since sm to SM to sm and sm to sM to sm sequences are observed.

Peter A. Peterson

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