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Archives of Industrial Biotechnology | Volume 2
May 14-15, 2018 | Montreal, Canada
World Yeast Congress
T
he native 2-micron plasmid of yeast is remarkable for
its nearly chromosome-like stability. This selfish DNA
element is optimized for its maintenance at an average copy
number of 40-60 molecules per cell nucleus. A plasmid coded
partitioning system, comprised of two partitioning proteins
and a cis-acting partitioning locus is responsible ensuring the
equal or nearly equal segregation of replicated plasmid copies
into mother and daughter nuclei. Cumulative results from a
variety of genetic, cell biological and biochemical experiments
suggest that the partitioning proteins promote the physical
association of plasmid molecules to yeast chromosomes. This
chromosome tethering is reminiscent of a similar strategy used
by the episomes of mammalian gamma herpes and papilloma
viruses for propagation in infected cells during long-term
latency. Our analyses using fluorescence-tagged single-copy
derivatives of the 2-micron plasmid suggest that plasmid sisters
formed by replication tether to sister chromatids in a symmetric
fashion, thus elevating the plasmid to nearly chromosome
status in 1:1 segregation. We are currently mapping potential
plasmid-localizing sites on chromosomes using genome-wide
approaches
Speaker Biography
Jayaram’s research is focused on the
Saccharomyces cerevisiae
plasmid 2-micron
circle—a small, high-copy extrachromosomal selfish DNA element with chromosome-
like stability. Plasmid persistence is accomplished by a deceptively simple partitioning
system consisting of two plasmid-coded proteins and a cis-acting partitioning locus.
The partitioning system promotes the tethering of plasmid sisters formed by replication
to sister chromatids, and 1:1 plasmid segregation by a hitchhiking mechanism. Copy
number maintenance utilizes DNA amplification promoted by the plasmid-coded
Flp site-specific recombinase. Amplification is initiated by a replication-coupled
DNA inversion reaction. Plasmid gene expression circuitry is fine-tuned for prompt
amplification response when needed, without the risk of runaway increase in copy
number. Our research interests span mechanisms of (a)DNA rearrangements mediated
by Flp and other site-specific recombinases, (b)chromosome-coupled plasmid
segregation, and (c)
in vivo
regulation of Flp levels/activity to prevent inappropriate
plasmid amplification. In summary, we wish to unveil the interplay of plasmid- and
host-encoded mechanisms that promote their nearly conflict-free coexistence over
evolutionary times.
e:
jayaram@austin.utexas.eduMakkuni Jayaram
University of Texas at Austin, USA
The yeast plasmid: A hitchhiker on chromosomes