The 3 biological domains delineated based on small subunit ribosomal RNAs (SSU rRNAs) are confronted by uncertainties regarding the relationship between Archaea and Bacteria, and the origin of Eukarya. The similarities between the paralogous valyl-tRNA and isoleucyl-tRNA synthetases in 5398 species estimated by BLASTP, which decreased from Archaea to Bacteria and further to Eukarya, were consistent with vertical gene transmission from an archaeal root of life close to Methanopyrus kandleri through a Primitive Archaea Cluster to an Ancestral Bacteria Cluster, and to Eukarya. The predominant similarities of the ribosomal proteins (rProts) of eukaryotes toward archaeal rProts relative to bacterial rProts established that an archaeal parent rather than a bacterial parent underwent genome merger with bacteria to generate eukaryotes with mitochondria. Eukaryogenesis benefited from the predominantly archaeal accelerated gene adoption (AGA) phenotype pertaining to horizontally transferred genes from other prokaryotes and expedited genome evolution via both gene-content mutations and nucleotidyl mutations. Archaeons endowed with substantial AGA activity were accordingly favored as candidate archaeal parents. Based on the top similarity bitscores displayed by their proteomes toward the eukaryotic proteomes of Giardia and Trichomonas, and high AGA activity, the Aciduliprofundum archaea were identified as leading candidates of the archaeal parent. The Asgard archaeons and a number of bacterial species were among the foremost potential contributors of eukaryotic-like proteins to Eukarya.

基于小亚基核糖体 RNA (SSU rRNA) 划分的 3 个生物域面临着古细菌和细菌之间的关系以及真核生物起源的不确定性。BLASTP估计的5398个物种中旁系同源缬氨酰-tRNA和异亮氨酰-tRNA合成酶之间的相似性，从古细菌到细菌，再到真核生物，与接近Methanopyrus kandleri的古细菌生命根通过原始基因的垂直基因传递一致。古细菌簇到祖先细菌簇，再到真核生物。真核生物的核糖体蛋白 (rProts) 与古菌 rProts 相对于细菌 rProts 的主要相似性表明，古菌亲本而不是细菌亲本与细菌进行基因组合并，产生具有线粒体的真核生物。真核发生受益于主要古菌加速基因采用（AGA）表型，该表型涉及来自其他原核生物的水平转移基因，并通过基因内容突变和核苷酸突变加速基因组进化。因此，具有大量 AGA 活性的古菌被视为候选古菌亲本。根据其蛋白质组与贾第鞭毛虫和毛滴虫的真核蛋白质组显示的最高相似性比特分数以及高 AGA 活性，Aceduliprofundum古细菌被确定为古细菌亲本的主要候选者。阿斯加德古菌和许多细菌物种是真核生物类真核蛋白的最重要的潜在贡献者。