Biochemical consequences of the insertion of a suppressor-mutator (Spm) receptor at the bronze-1 locus in maize.

Transposition of a receptor element (Rs) for the suppressor-mutator (Spm) has generated the first Spm-controlled mutable allele of the bronze-1 (bz) locus in maize (Zea mays L.). In the absence of Spm, bz-m13 conditions full anthocyanin pigmentation in the aleurone but has a markedly decreased level compared to wild type of the gene product, UDPglucose:flavonol 3-O-glucosyltransferase (UFGT; EC 2.4.1.91). This UFGT activity appears to be qualitatively similar to the wild-type enzyme. Throughout endosperm development, the amount of a crossreactive material far exceeds the amount of detectable UFGT activity. This and other observations suggest that this insertion of Rs leads to the production of two polypeptides from the bz-m13 allele.