131Synthetic Biology: Parts, Devices and Applications, First Edition. Edited by Christina Smolke.
© 2018 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2018 by Wiley-VCH Verlag GmbH & Co. KGaA.
7
Most human genes are interrupted by one or more introns that have to be
removed to generate mRNAs with intact open reading frames (ORFs), a process
called pre-mRNA splicing. A ribonucleoprotein complex, the spliceosome, is
responsible for the accurate removal of the intervening sequences. Alternative
splicing, that is, not all exons are included in the mature mRNA every time, cre-
ates the possibility that one gene can encode for more than one protein. This
immensely increases the coding capacity of a genome. In humans, aberrant splic-
ing has been recognized to be the causative agent of several hereditary diseases
and to drive cancer progression. In contrast to humans, introns are rare in bud-
ding yeast but seem to be important for fine-tuning gene expression and growth
under stress conditions.
7.1 The Discovery of “Split Genes”
In 1977, Richard J. Roberts and Phillip A. Sharp studied adenovirus type 2, a
double-stranded DNA virus causing common cold. Their aim was to map the
location of the genes on the viral genome. Unexpectedly, they found that the
mRNA did not hybridize to the DNA in a continuous stretch. Instead, it hybrid-
ized to four neighboring segments in the genome, separated by three intervening
sequences. These intervening sequences were looped out in the DNA as they
were missing in the mRNA sequence [1, 2]. This came as a surprise, as former
analyses of bacterial genes suggested that a gene comprises a continuous stretch
of DNA. Soon after this initial discovery, this discontinuous gene structure was
shown to be a common feature of eukaryotic genes. Sixteen years later, both were
awarded the Nobel Prize in Physiology or Medicine for their discovery of “split
genes.”
The realization that eukaryotic genes are comprised of exons (sequences of a
gene included into the mature mRNA) and introns (intervening sequences
removed upon splicing) called for a new mRNA maturation process: the removal
of the intronic sequences from the pre-mRNA to yield a shortened mature
7 Splicing and Alternative Splicing Impact on Gene Design
on Gene Design
Beatrix Suess, Katrin Kemmerer, and Julia E. Weigand
Department of Biology, Technische Universität Darmstadt, Schnittspahnstraße 10, 64287 Darmstadt, Germany