CHARACTERIZATION OF THE MAJOR TRANSCRIPTS ENCODED BY THE REGULATORY MUDR TRANSPOSABLE ELEMENT OF MAIZE

The MuDR element controls the transposition of the Mutator transposabl e element family in maize. Previous studies reported the presence of t wo major MuDR-homologous transcripts that correlate with Mutator activ ity. In this study, we describe the structure and processing of these two major transcripts. The transcripts are convergent, initiating from opposite ends of the element within the 220-bp terminal inverted repe ats. The convergent transcripts do not overlap, and only 200 bp of int ernal MuDR sequences are not transcribed. Cloning and sequencing of mu ltiple MuDR cDNAs revealed unusual intron/exon junctions, differential splicing, and multiple polyadenylation sites. RNase protection experi ments indicated that some splicing failure occurs in young seedlings, and that a low level of antisense RNA exists for both transcripts. On a whole plant level, the presence of the major MuDR transcripts strict ly correlates with Mutator activity in that no MuDR transcripts are ob served in non-Mutator or inactive Mutator stocks. Examination of vario us tissues from active Mutator stocks indicates that the two transcrip ts are present in all organs and tissues tested, including those with no apparent transposition activity. This suggests that Mutator activit y is not simply controlled by the level of the major MuDR transcripts.