Synthesis, cloning and sequencing of glucoamylase cDNA from Aspergillus niger mutant T21.

Poly(A)+ RNA was isolated from Aspergillus niger T21, a glucoamylase overproducing strain and was used as template to synthesize double stranded cDNA. A cDNA library was then constructed. The E. coli transformants were screened for the glucoamylase cDNA by in situ colony hybridization with P-labeled fragment of glucoamylase gene as probe. The positive rate was 1.6%. Restriction analysis proved that 32% of the positive clones carried the inserts of 2.1 kb of full length glucoamylase cDNA. Sequence of the glucoamylase cDNA was determined and the result showed that the sequence of glucoamylase gene of the mutant T21 was almost the same as that reported previously. The high rate of glucoamylase cDNA-containing clones in the cDNA library of strain T21 provided evidence of high steady state level of glucoamylase mRNA in mycelium of mutant T21. Most likely it is one of the major causes for the high glucoamylase productivity of mutant T21.