Project description:We designed and synthesized synI, which is ~21.4% shorter than native chrI, the smallest chromosome in Saccharomyces cerevisiae. SynI was designed for attachment to another synthetic chromosome due to concerns surrounding potential instability and karyotype imbalance, and is now attached to synIII, yielding the first synthetic yeast fusion chromosome. We constructed additional fusion chromosomes to investigate effects of fusions on nuclear function. We observed unexpected loops and twisted structures in chrIII-I and chrIX-III-I fusion chromosomes dependent on silencing protein Sir3. ChrI faces special challenges in assuring meiotic crossovers required for efficient homolog disjunction. Centromere deletions engineered into fusion chromosomes revealed opposing effects of core centromeres and pericentromeres in modulating deposition of meiotic recombination protein Red1. These effects extended over >100kb, to disproportionally promote meiotic recombination of small chromosomes like chrI. These findings reveal the power of synthetic genomics to uncover new biology and deconvolute complex biological systems.
Project description:Whether synthetic genomescan power life has attracted broad interest in the synthetic biology field, especially when the synthetic genomes are extensively modified with thousands of designer features. Here we reportde novosynthesis of the largest eukaryotic chromosome thus far, synIV, a 1,454,621-bpSaccharomyces cerevisiaechromosome resulting from extensive genome streamlining and modification. During the construction ofsynIV, we developed megachunk assembly combined with a hierarchical integration strategy, which significantly increased the accuracy and flexibility of synthetic chromosome construction and facilitated chromosome debugging. In addition to the drastic sequence changes made to synIV by rewriting it, we further manipulated the three-dimensional structure of synIV in the yeast nucleus to explore spatial gene regulation within the nuclear space. Surprisingly, we found few gene expression changes, suggesting that positioning inside the yeast nucleoplasm plays a minor role in gene regulation. Lastly, we tethered synIV to the inner nuclear membrane via its hundreds of loxPsym sites and observed transcriptional repression of the entire chromosome, demonstrating chromosome-wide transcription manipulation without changing the DNA sequences. Our manipulation of the spatial structure of the largest synthetic yeast chromosome shed light on higher-order architectural design of the synthetic genomes.