6'-MERCAPTOGUANOSINE-RESISTANCE IS RELATED WITH PURF GENE ENCODING 5'-PHOSPHORIBOSYL-1'-PYROPHOSPHATE AMIDOTRANSFERASE IN INOSINE-5'-MONOPHOSPHATE OVERPRODUCING BREVIBACTERIUM-AMMONIAGENES

From the gene library constructed with the chromosomal DNA of 6'-merca ptoguanosine (MGS)-resistant strain Brevibacterium ammoniagenes IPR-1, a DNA fragment which conferred MGS-resistance to the wild-type strain B. ammoniagenes ATCC6872 was cloned. The purF gene encoding 5'-phosph oribosyl-1'-pyrophosphate amidotransferase was identified from this fr agment and its nucleotide sequence was determined. Wild type purF gene was also cloned by polymerase chain reaction using chromosomal DNA of ATCC6872 as the template and its sequence was determined. Two nucleot ides, 583 'A' and 1065 'A', of MGS-resistant purF gene had been change d from 583 'G' and 1065'G' by mutagenesis, respectively. Both changes at position 583 and 1065 were proved to be responsible for MGS-resista nce by site-directed mutagenesis.