The Long and Short of Synaptonemal Complex Assembly: Investigating the genesis and functional relevance of a smaller Zip1 isoform

Abstract

The proper segregation of homologous chromosomes (homologs) during meiosis is a paramount task for living cells. Homologs successfully disjoin from one another on the meiosis I spindle so long as they have undergone prior alignment and have formed at least one crossover attachment. The Zip1 protein promotes an intimate alignment between homologs during budding yeast meiosis through its role as a building block of the synaptonemal complex (SC), a proteinaceous structure that assembles along the full length of aligned partner chromosomes. Independent of its role in building SC, Zip1 also plays a critical role in promoting interhomolog crossover recombination, although the molecular underpinnings of this activity are unclear. Through a structure‐function study to identify residues that are essential for Zip1's crossover recombination or SC assembly functions, we identified two zip1 mutants that produce an unexpectedly smaller form of Zip1. In meiotic cells that express either a zip1 allele in which six contiguous residues are changed to alanine, or an allele in which only two of the aforementioned six residues are changed to alanine, a large fraction of Zip1 migrates on a protein gel as if it has lost ten kilodaltons of its wild‐type molecular weight. The change in apparent molecular weight of Zip1 observed in our mutants raises the unanticipated possibility that most Zip1 proteins within the wild‐type meiotic cell are constitutively modified, perhaps by a ten kilodalton protein, and that this post‐translational modification is dependent on the residues that are altered in our two zip1 mutant alleles. Here we describe the results of two experiments designed to ask whether Zip1 in wild‐type meiotic nuclei is constitutively modified by the SUMO protein. First, we will examine the apparent size of Zip1 protein when two SUMO ligase proteins, Siz1 and Siz2, are simultaneously removed. Second, we will determine whether Zip1's molecular weight appears increased in a strain that expresses a larger molecular weight version of SUMO, 3xHA‐SUMO. Finally, we will examine SC assembly and crossover recombination in the two zip1 mutant strains that produce the putative unmodified form of Zip1, in order to determine a function for this potential post‐translational modification.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.