Y. Kumano et J. Nikawa, FUNCTIONAL-ANALYSIS OF MUTATIONS IN THE PIS GENE, WHICH ENCODES SACCHAROMYCES-CEREVISIAE PHOSPHATIDYLINOSITOL SYNTHASE, FEMS microbiology letters, 126(1), 1995, pp. 81-84
The PIS gene for an enzyme phosphatidylinositol synthase having an inc
reased K-m for myo-inositol, was isolated from Saccharomyces cerevisia
e. The mutant PIS gene contained a CAA codon at position 114 instead o
f the CAC codon observed in the wild-type gene, resulting in alteratio
n of the amino acid from His to Gln. Oligonucleotide mediated site-dir
ected mutagenesis of PIS at codon 114 revealed that mutant genes with
codons for Ala, Thr and Leu could support yeast eel growth in vivo, bu
t those, for Asp, Lys and Tyr could not. All mutant enzymes when expre
ssed in Escherichia coli showed greatly reduced in vitro activity.