This review provides a comprehensive update of the advances in discovery, biosynthesis, and engineering of ribosomally-synthesized and post-translationally modified peptides (RiPPs).

Integral β-barrel proteins are found in the outer membranes of mitochondria, chloroplasts, and Gram-negative bacteria. The machine that assembles these proteins contains an integral membrane protein, called YaeT in Escherichia coli , which has one or more polypeptide transport–associated (POTRA) domains. The crystal structure of a periplasmic fragment of YaeT reveals the POTRA domain fold and suggests a model for how POTRA domains can bind different peptide sequences, as required for a machine that handles numerous β-barrel protein precursors. Analysis of POTRA domain deletions shows which are essential and provides a view of the spatial organization of this assembly machine.

Bring Out the β-Barrel: The assembly of β-barrel membrane proteins, which are found in the outer membrane of Gram-negative bacteria and in the mitochondria and chloroplasts of eukaryotes, is poorly understood. Now Hagan et al. (p. 890 , published online 8 April; see the Perspective by Stroud et al. ) describe the development of a reconstituted system that recapitulates the process of assembly of β-barrel membrane proteins by the Escherichia coli Bam complex. The assembly of a protein substrate required the purified five-protein Bam complex and several subcomplexes and a chaperone, but did not require an external input of energy.

Directed evolution has revolutionized biomolecular engineering by applying cycles of mutation, amplification and selection to genes of interest (GOIs). However, classical directed evolution methods that rely on manually staged evolutionary cycles constrain the scale and depth of the evolutionary search that is possible. We describe genetic systems that achieve cycles of rapid mutation, amplification and selection fully inside living cells, enabling the continuous evolution of GOIs as cells grow. These systems advance the scale, evolutionary search depth, ease and overall power of directed evolution and access important new areas of protein evolution and engineering.