FUNGAL GENETICS, MOLECULAR GENETICS, AND GENOMICS 163
Fig. 9.3Ty elements of yeast. (a) The Ty element consists of an epsilon region which encodes its own replication, flanked
by delta sequences. Copies of the transposon are then inserted elsewhere in the same or in other chromosomes.
(b) The delta regions of one Ty element can undergo homologous recombination, leading to a “solo delta” in the
chromosome. (c) Homologous recombination between two Ty elements on a chromosome could lead to excision of
part of the chromosome. (d) Homologous recombination between Ty elements on different chromosomes could create
hybrid chromosomes. (Based on Oliver 1987.)
discovered in other fungi, and by the 1980s they were
known in over 150 species, including representatives
of all the major fungal groups (Buck 1986). With a few
notable exceptions, however, the presence of VLPs is not
associated with any obvious disorder, so most fungal
viruses seem to be symptomless.
Studies on a range of fungi have shown that fungal
viruses (or VLPs) have similar basic features (Fig. 9.4).
- They are isometric particles, 25 –50 nm diameter,
with a genome of double-stranded RNA (dsRNA), a
capsid composed of one major polypeptide, and
they code for a dsRNA-dependent RNA polymerase
for replication of the viral genome. - The genome size is variable. Even within a single
fungus it ranges from about 3.5 to 10 kb. In some
cases this variation is due to internal deletions of a