To begin genome-wide functional analysis, we analysed the consequences of d
eleting each of the 265 genes of chromosome VIII of Saccharomyces cerevisia
e. For 33% of the deletion strains a growth phenotype could be detected: 18
% of the genes are essential for growth on complete glucose medium, and 15%
grow significantly more slowly than the wild-type strain or exhibit a cond
itional phenotype when incubated under one of 20 different growth condition
s. Two-thirds of the mutants that exhibit conditional phenotypes are pleiot
ropic; about one-third of the mutants exhibit only one phenotype. We also m
easured the level of expression directed by the promoter of each gene. Abou
t half of the promoters direct detectable transcription in rich glucose med
ium, and most of these exhibited only low or medium activity. Only 1% of th
e genes are expressed at about the same level as ACT1. The number of active
promoters increased to 76% upon growth on a non-fermentable carbon source,
and to 93% in minimal glucose medium. The majority of promoters fluctuated
in strength, depending on the medium. Copyright (C) 1999 John Wiley & Sons
, Ltd.