THE TRANSPOSABLE ELEMENT TAN1 OF ASPERGILLUS-NIGER VAR AWAMORI, A NEWMEMBER OF THE FOT1 FAMILY

Aspergillus niger var. awamori has transposable elements that we refer to as Vader and Tan1 (transposon A. niger). Vader was identified by s creening unstable nitrate reductase (niaD) mutants for insertions. Fou r of the isolated niaD mutants were shown to contain a small insertion element. This 437 bp insertion element, Vader, is flanked by 44 bp in verted repeats (IR) and is present in approximately 15 copies in the g enomes of two A. niger strains examined. A synthetic 44 bp oligomer of the inverted repeat of Vader has now been used to clone, via the poly merase chain reaction, a 2.3 kb Tan1 element. The Tan1 element has als o been isolated from a partial genomic library. Tan1 is present as a s ingle copy in A. niger var. awamori. The Tan1 element has a unique org anization: IR-ORF-IR-IR-Vader-IR. The single open reading frame (ORF) (1668 bp) encodes a putative transposase homologous to Fusarium oxyspo rum Fot1 and Magnaporthe grisea Pot2. Immediately 3' to the second inv erted repeat, which bounds the transposase, is a copy of the AT-rich V ader element. We hypothesize that at some stage the independent Vader element, although inactive by itself, arose from Tan1, resulting in cu rrent strains with only one copy of Tan1 providing transposase activit y and numerous mobile copies of Vader dispersed in the genome.