A Life with Yeast Molecular Biology - Prof. Dr. Horst Feldmann

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H. FELDMANN
the UV-light technique [47]. Clearly, the transcriptional units
were no longer than 200 bp for almost all of the 13 tRNA species
tested and we concluded that these tRNA genes are scattered
throughout the genome in singular entities. In 1978, we began
to investigate the genomic organization of yeast tRNA genes at
the molecular level. This became feasible only when we had
adopted the genetic engineering techniques developed from the
mid-1970s on.
The beginning of genetic engineering undoubtedly was the
successful approach of Paul Berg and his collaborators to show
that recombinant DNA could be maintained in a host cell [48].
I vividly remember a long night session with full moon in the
courtyard of a monastery at the Summer School 1971 held in
Erice, where Berg, Sanger, and Tomkins chaired a discussion on
the three paradigm shifts initiating a revolution in Molecular
Biology: the discovery and use of restriction enzymes [49–51]; the
utilization of recombinant DNA; and the necessity for developing
methods allowing the determination of long DNA sequences,
which had to follow principles different from the ones applied
to the sequencing of RNA and became reality in the years to
follow [52–54].
Though since 1972, several methods had been developed for
cloning and characterization of recombinant DNA molecules, it
was only after the Asilomar Conference on Recombinant DNA
[55] that safe and simple procedures and bacterial vehicles could
be propagated for extensive use of cloning recombinant DNA
molecules. A big advantage of cloning vehicles based on phage
lambda was the larger size of DNA sequences that could be
accommodated. Those latter properties were shared by the
cosmids, plasmid gene-cloning vectors packageable in phage
lambda heads. These methods were applied to yeast genes, too.
The transformation of yeast cells by replicating hybrid plasmids,
however, was the first successful transformation of a eukaryotic
cell and marked a break-through for yeast molecular biology
[56,57].
Our first approach to clone various tRNA genes from yeast was
only semi-selective and largely followed conventional cloning
techniques, but our aim was clear: we wanted to study the
structure and genomic environment of these genes and learn how
they are expressed. Judith Olah coming as a post-doc was to
initiate this work [58]. Unfortunately, in October 1979 an