More than a decade ago, attempts were made to clone and
express various bacterial xylose isomerase genes in S. cerevi-
siae, but these attempts failed to produce any recombinant
Saccharomyces strains that were able to ferment xylose or uti-
lize this sugar for growth. In this paper, we describe the devel-
opment of a group of high-copy-number recombinant plas-
mids, collectively designated the pLNH plasmids (pLNH31,
pLNH32, pLNH33, and pLNH34), that can transform some of
the best glucose-fermenting Saccharomyces strains into effec-
tive xylose-fermenting yeasts which can also effectively utilize
xylose for aerobic growth.