Molecular analysis of the Doppia transposable element of maize

Doppia (Dop) transposable elements were first identified from element termi ni found in the upstream portions of certain alleles of the pl1 and r1 loci of maize. At the r1 locus, these Dop end sequences are present in a region called sigma, which functions as the promoter for the S genes of the R-r h aplotype, and which is required for efficient epigenetic modification of th e S genes during paramutation. In order to better understand the significan ce of the Dop element sequences at R-r, and to investigate the Dop-encoded products that might regulate r1 genes in this haplotype, we have cloned a m ore complete Dop element, Dop4. The Dop4 element can encode two proteins th at have strong sequence similarity to the TnpA and TnpD proteins of the wel l characterized maize transposable element En/Spm. The DOPA protein, which is similar to TnpA of En/Spm, is shown to bind to short, subterminal repeat motifs located in the Dop element ends. Like TnpA, DOPA promotes intermole cular associations between DNA molecules. In contrast to the activity of Tn pA, which is a transcriptional repressor of En/Spm, DOPA activates expressi on of reporter genes driven by either the Dop promoter or sigma in transien t expression assays.