Nucieotide sequence of the maize transposable elementMul

Abstract

A cloned DNA fragment from the maize allele Adhl-S3034 contains all of Mul, an insertion element involved in Robertson's Mutator activity. The element is 1367 base pairs (bp) long and is flanked by nine bp direct repeats of insertion site DNA. It has inverted terminal repeats of 215 and 213 bp showing 95% homology. Within the element are two direct repeats of 104 bp showing 96% homology. Four open reading frames (ORFs) were found, two in each DNA strand. Mul can be divided into two halves, each containing one terminal inverted repeat, an internal direct repeat, and two overlapping ORFs. The GC content of each half is high (70%), while that of a central 60 base portion of the element is low (26%). The central region contains the only sequence resembling the TAATA Goldberg and Hogness eukaryotic promoter signal. Multiple copies of DNA sequences related to Mul found in Mutator maize plants are generally similar in organization to the cloned element. A larger version containing a discrete 300 to 400 base pair insertion was found in some Mutator lines.

DNA modification of a maize transposable element correlates with loss of activity.

“…A mutation in the alcohol dehydrogenase 1 (Adhl) gene was isolated from a Mutator stock and shown to contain an 41.4-kilobase (kb) DNA insertion (2). This element, designated Mul, has terminal inverted repeats characteristic of a transposable element (3,4). Two size classes of elements homologous to Mul are observed in most Mutator lines; the =1.4-kb Mul size class and an 1.7-kb size class (4) termed Mul.7 (5).…”

An extrachromosomal form of the Mu transposons of maize.

“…Therefore, the concentration of extrachromosomal Mul is estimated to be 0. 6 Electron Microscopy (EM). To prepare the ccDNA fractions for EM we extracted DNA from -80 g of immature tassels of Mu-active plants by the described procedure appropriately scaled upward.…”

“…5). Tn Mu) has been sequenced and found to have 200-base-pair (bp) terminal inverted repeats, 100-bp internal direct repeats, and four open reading frames of 300-500 bp (6). Although Mu) is an unusually active transposon-about 1/4 to 1/2 of the Mu) elements are found at new chromosomal locations in the outcross progeny (7)-little is known about the mechanism of transposition, and as yet no mRNA or transposase proteins have been identified.…”

Maize Mutator transposon

“…All subfamilies share 170-220 bp conservative terminal inverted repeats (TIRs), and their internal sequences are distinct (Lisch, 2002). The 1367-bp Mu1 has the highest copy number and mutation rate (Barker et al, 1984). The Cy/bz-rcy locus first identified by Schnable and Peterson (1989) is classified as the Mu7 subfamily.…”