L-Asparagine auxotrophs of Saccharomyces cerevisiae: genetic and phenotypic characterization

Abstract

L-Asparagine auxotrophy in Saccharomyces cerevisiae is the result of mutation in each of two unlinked cistrons, ASN1 and ASN2. Mutation in only one of these cistrons yields growth indistinguishable from that of wild-type cells under a variety of nutritional stresses. Relatively high concentrations of L-asparagine are required to permit maximal growth of the auxotrophs, and the amino acid requirement cannot be satisfied by a variety of other amino acids that serve as nitrogen sources for cell growth. Although reversion of the mutations can occur, haploid populations of cells containing only low frequencies of prototrophs can be maintained easily. In diploid cells heteroallelic for certain combinations of alleles of the two genes, mitotic recombination gives rise to prototrophic cells that accumulate to high frequency in populations of the cells.

Cloning of the ASN1 and ASN2 genes encoding asparagine synthetases in Saccharomyces cerevisiae: differential regulation by the CCAAT‐box‐binding factor

“…This double disruption leads to total auxotrophy for asparagine (data not shown). This result confirms that a double mutant is required in yeast to obtain asparagine auxotrophy (Jones, 1978;Ramos and Wiame, 1979).…”

“…Isogenic wild-type and disrupted strains were tested for growth in the absence of asparagine, and no growth defect could be detected in the asn1 or asn2 mutant strains (data not shown). These results are in agreement with those from Jones (1978) who could not find any growth defect associated with the asn1 or asn2 single mutants. In another report, Ramos and Wiame (1979) observed that an asnA mutation leads to a partial auxotrophy while asnB mutants were totally prototrophic.…”

“…In S. cerevisiae, asparagine auxotrophy is the result of mutations at two unlinked loci, asn1 and asn2 (Jones, 1978), most probably allelic to the asnA and asnB loci described by Ramos and Wiame (1979). We used an asnA asnB double mutant derived from strain S 8539 (asnA asnB) to isolate the wild-type ASN1 and ASN2 genes by complementation of the asparagine requirement of this double mutant on minimal medium.…”

“…Z48675), revealing a unique ORF which encodes a polypeptide of 572 residues with a predicted molecular weight of c. 65 kDa. This sequenced gene was, for convenience, named ASN1, but it is not necessarily the same as the asn1 locus described by Jones (1978). The partial nucleotide sequence from the 30C1 fusion was found to be 100% identical to the 3' end of the ASN1 gene, confirming that 30C1 is an ASN1-lacZ fusion.…”

“…In yeast, previous genetical studies have shown that mutations at two unlinked loci are required for asparagine auxotrophy. These loci, named asnA and asnB by Ramos and Wiame (1979), are probably the same as the asn1 and asn2 loci described by Jones (1978).…”