A Zip3-like protein plays a role in crossover formation in the SC-less meiosis of the protist Tetrahymena

Mol Biol Cell. 2017 Mar 15;28(6):825-833. doi: 10.1091/mbc.E16-09-0678. Epub 2017 Jan 18.


When programmed meiotic DNA double-strand breaks (DSBs) undergo recombinational repair, genetic crossovers (COs) may be formed. A certain level of this is required for the faithful segregation of chromosomes, but the majority of DSBs are processed toward a safer alternative, namely noncrossovers (NCOs), via nonreciprocal DNA exchange. At the crossroads between these two DSB fates is the Msh4-Msh5 (MutSγ) complex, which stabilizes CO-destined recombination intermediates and members of the Zip3/RNF212 family of RING finger proteins, which in turn stabilize MutSγ. These proteins function in the context of the synaptonemal complex (SC) and mainly act on SC-dependent COs. Here we show that in the SC-less ciliate Tetrahymena, Zhp3 (a protein distantly related to Zip3/RNF212), together with MutSγ, is responsible for the majority of COs. This activity of Zhp3 suggests an evolutionarily conserved SC-independent strategy for balancing CO:NCO ratios. Moreover, we report a novel meiosis-specific protein, Sa15, as an interacting partner of Zhp3. Sa15 forms linear structures in meiotic prophase nuclei to which Zhp3 localizes. Sa15 is required for a wild-type level of CO formation. Its linear organization suggests the existence of an underlying chromosomal axis that serves as a scaffold for Zhp3 and other recombination proteins.

MeSH terms

  • Cell Cycle Proteins / metabolism
  • Chromosomal Proteins, Non-Histone / metabolism
  • Crossing Over, Genetic / physiology
  • DNA Breaks, Double-Stranded
  • DNA Repair / physiology
  • DNA-Binding Proteins / metabolism
  • Meiosis / physiology
  • RING Finger Domains
  • Recombination, Genetic / physiology
  • Synaptonemal Complex / metabolism*
  • Tetrahymena / metabolism


  • Cell Cycle Proteins
  • Chromosomal Proteins, Non-Histone
  • DNA-Binding Proteins