The endoamylolyric enzyme or-amylasc (EC2 3.2.1.1 ,cu-1, 4-glucan-4-~lucnnohydrolasc) catalyses rhe cleavage of cu-1,4~glycosidic bonds within starch and related substrates releasitlg nlalrose and lorlger oligosaccharides ntld a-limit dcxtrins. A wide range of organisms produec ol-amylases and several of the relcvant genes have been cloned [I-d]

Two genes (SCRI and SCR2) encoding natural cycloheximide resistance in the budding yeast Schwanniomyces occidentalis have been cloned by expression in Saccharomyces cerevisiae. Both genes determine resistance to the inhibitory action of cycloheximide on the ribosome. SCRl and SCR2 are present as single copies in Schwanniomyces occidentalis, where they map on chromosomes I1 and V, respectively. The nucleotide sequence of SCR2 contains an open reading frame of 321 nucleotides which is interrupted by an intron of 452 nucleotides. It encodes a polypeptide of 106 amino acids of molecular mass 12.25 kDa and PI 11.19. The deduced amino acid sequence shows a high degree of similarity to the LA1 protein of the 60s ribosomal subunit from several eukaryotic organisms. The intron and the 5' non-coding region of SCR2 possess conserved elements which are typical of yeast ribosomal protein genes. A single amino acid change determines the resistance or sensitive phenotype to cycloheximide of the 80s ribosome since replacement of Gln56 in LA1 from Schwanniomyces with Pro, by site-directed mutagenesis, confers cycloheximide sensitivity. SCR2 may serve as a practical yeast cloning marker if integrated in a multicopy plasmid. [l] is a budding yeast which has attracted the attention of researchers because it secrets a variety of high-molecular-mass proteins. These include a-amylase and a glucoamylase which also shares a starch debranching activity. Therefore it solubilizes starch by complete hydrolysis to glucose [2]. Because of the potential industrial importance of this yeast, it is desirable to characterize in detail its genetic constitution and its spectrum of sensitivity or resistance to antibiotics. Indeed Sw. occidentalis is highly resistant in vivo to inhibition by the glutarimide antibiotic cycloheximide (cyh) [3], which blocks polypeptide chain elongation by eukaryotic ribosomes (for reviews, see [4,51). This resistance is also shared by certain other yeast species including Kluyveromyces lactis and K. fragilis [6, 71, Candida maltosa and C. tropicalis [8, 91. In Saccharomyces cerevisiae, mutations at five different loci induce resistance to cyh [lo, 111. Of these, only cyh2 has been subjected to detailed biochemical and genetic studies. The presence of this gene confers resistance to cyh levels of 50-70 pg/ml. The gene encodes an altered ribosomal protein L29 which is presumed to reduce the affinity of the 60s ribosomal subunit for cyh [12, 131. The cyh2 gene has been Correspondence to A. Schwanniomyces occidentalis

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