All known living organisms use at least 20 amino acids as the basic building blocks of life. Efforts to reduce the number of building blocks in a replicating system to below the 20 canonical amino acids have not been successful to date. In this work, we use filamentous phage as a model system to investigate the feasibility of removing methionine (Met) from the proteome. We show that all 24 elongation Met sites in the M13 phage genome can be replaced by other canonical amino acids. Most of these changes involve substitution of methionine by leucine (Leu), but in some cases additional compensatory mutations are required. Combining Met substituted sites in the proteome generally led to lower viability/infectivity of the mutant phages, which remains the major challenge in eliminating all methionines from the phage proteome. To date a total of 15 (out of all 24) elongation Mets have been simultaneously deleted from the M13 proteome, providing a useful foundation for future efforts to minimize the genetic code.

所有已知的生物都至少使用20种氨基酸作为生命的基本组成部分。迄今为止，将复制系统中构件的数量减少到20种以下规范氨基酸的努力尚未成功。在这项工作中，我们使用丝状噬菌体作为模型系统来研究从蛋白质组中去除蛋氨酸（Met）的可行性。我们显示，M13噬菌体基因组中的所有24个延伸Met位点都可以被其他规范氨基酸取代。这些变化大多数涉及用亮氨酸（Leu）取代甲硫氨酸，但在某些情况下，还需要其他补偿性突变。结合蛋白质组中的Met取代位点通常会导致突变型噬菌体的活力/感染性降低，这仍然是从噬菌体蛋白质组中消除所有蛋氨酸的主要挑战。