We have cloned the met2 gene from Ascobolus immersus by heterologous hybridization with the MET2 gene of Saccharomyces cerevisiae. This gene codes for the homoserine O-transacetylase, one of the methionine biosynthetic enzymes. The complete nucleotide sequence of a 2910-bp DNA fragment carrying the met2 gene has been determined. The gene contains a 165-bp intron which is similar in structure to other fungal introns. The deduced amino acid (aa) sequence (518 aa residues; Mr of 57726) shows three domains with a significant level of homology with the corresponding yeast protein. Northern-blot analysis reveals at least two transcripts (2.4 and 2.1 kb) probably due to transcription termination heterogeneity, as suggested by S1-mapping experiments. Polymorphism has been observed in the met2 gene flanking regions of Ascobolus strains from two different stocks.
A 5.1-kb DNA fragment from Saccharomyces cerevisiae, which complements a yeast met2 mutant strain, has been cloned. This fragment contains the wild-type MET2 gene which codes for the homoserine O-transacetylase, one of the methionine biosynthetic enzymes. The presence of the MET2 gene has been shown by integrative transformation experiments and genetic analyses of the resulting transformants. The complete nucleotide sequence of a 2826-bp DNA fragment carrying the MET2 gene has been determined. The sequence contains one major open reading frame of 438 codons, giving a calculated Mr of 48,370 for the encoded protein. We have identified the transcriptional product of the MET2 gene and estimated its size at 1650 nucleotides.
