A DNA comprising an adenylosuccinate synthetase gene region with a DNA fragment inserted to render said gene inactivated can be produced by the use of reombinant DNA techniques. Said DNA or a vector with said DNA is used to transform Bacillus strain capable of producing inosine and/or guanosine, and the thus obtained transofrmant is both high in inosine and/or guanosine accumulation and in stability.
