IDENTIFICATION AND CLONING OF A MOBILE TRANSPOSON FROM ASPERGILLUS-NIGER VAR AWAMORI

Aspergillus niger var. awamori contains multiple copies of a transposa ble element, Vader. This element was detected as a 437-bp insertion in four independently isolated spontaneous mutants of the niaD (nitrate reductase) gene. The Vader element is present in approximately 15 copi es in both A. niger var. awamori and A. niger. A single copy of Vader was detected from only one of the two laboratory strains of A. nidulan s which were also examined. Insertion of the Vader element into the ni aD gene of A. niger var. awamori caused a 2-bp duplication (TA) of the target sequence. The Vader element is flanked by a 44-bp inverted rep eat. The genetic stabilities of the inserted Vader elements at niaD we re examined by studying reversion frequencies resulting in colonies ab le to grow on nitrate as a sole nitrogen source. Mutants niaD392 and n iaD436 reverted at a frequency of 9 x 10(-3) and 4 x 10(-2), respectiv ely. Two of the mutants, niaD587 and niaD410, reverted at a lower freq uency of 6 x 10(-4).