RNA sequence (RNA-seq) profiling of synthesized chromosome SynI in Saccharomyces cerevisiae

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.我们设计并合成了synI（合成染色体I），其长度较酿酒酵母（Saccharomyces cerevisiae）中最小的天然染色体I（chrI）短约21.4%。鉴于潜在的不稳定性与核型失衡风险，synI被设计为可与另一合成染色体相连，目前它已与synIII（合成染色体III）相连，形成了首个酵母合成融合染色体。我们构建了额外的融合染色体，以探究染色体融合对细胞核功能的影响。我们观察到，依赖于沉默蛋白Sir3（silencing protein Sir3）的chrIII-I与chrIX-III-I融合染色体中存在意外出现的环状与扭曲结构。染色体I在确保高效同源染色体分离所需的减数分裂交换方面面临特殊挑战。通过工程手段在融合染色体中引入着丝粒缺失后，研究揭示了核心着丝粒与着丝粒旁区域在调控减数分裂重组蛋白Red1（meiotic recombination protein Red1）沉积过程中的相反作用。这类调控效应可延伸至超过100kb的范围，不成比例地促进了诸如染色体I这类小型染色体的减数分裂重组。上述发现展现了合成基因组学（synthetic genomics）在揭示全新生物学现象、厘清复杂生物系统方面的强大能力。