High impact information on Top3beta

• We previously found that Drosophila topo IIIbeta can relax plasmid DNA only if the DNA is first hypernegatively supercoiled [1].
• Whereas this mutation can be rescued by a Top3alpha transgene, ubiquitous overexpression of D. melanogaster topo IIIbeta cannot rescue this allele [2].
• The cleavage products require protease treatment to enter the gel, they are stable over time, they are reversible, and they are not observed with a Y332F active site mutant, which further supports the idea that topo IIIbeta possesses an endonucleolytic cleavage activity [3].
• The top3 cDNA encodes an 875-amino acid protein, which is nearly 60% identical to mammalian topoisomerase IIIbeta enzymes [4].
• The top3beta gene is a single-copy gene located at 5 E-F on the X chromosome [4].

Biological context of Top3beta

• Whereas top3beta truncation does not affect viability or fertility, wh null mutants display male sterile and female semi-sterile phenotypes [5].
• Through mutagenesis by P-element transposition, we identified a series of mutants with deletions in topoisomerase 3beta gene (top3beta) and an adjacent, previously uncharacterized gene CG15897, here named wuho (wh) [5].

Analytical, diagnostic and therapeutic context of Top3beta

• Southern blot analysis of the cleavage products demonstrates that the topo IIIbeta cleavage activity is concentrated primarily in highly A/T-rich regions [3].

References