DNA polymerase eta (Pol eta) is a eukaryotic lesion bypass polymerase that helps organisms to survive exposure to ultraviolet (UV) radiation, and tumor cells to gain resistance against cisplatin-based chemotherapy. It allows cells to replicate across cross-link lesions such as 1,2-d(GpG) cisplatin adducts (Pt-GG) and UV-induced cis-syn thymine dimers. We present structural and biochemical analysis of how Pol eta copies Pt-GG-containing DNA. The damaged DNA is bound in an open DNA binding rim. Nucleotidyl transfer requires the DNA to rotate into an active conformation, driven by hydrogen bonding of the templating base to the dNTP. For the 3'dG of the Pt-GG, this step is accomplished by a Watson-Crick base pair to dCTP and is biochemically efficient and accurate. In contrast, bypass of the 5'dG of the Pt-GG is less efficient and promiscuous for dCTP and dATP as a result of the presence of the rigid Pt cross-link. Our analysis reveals the set of structural features that enable Pol eta to replicate across strongly distorting DNA lesions.

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The intermolecular communication within NRPS complexes relies on the coordinated interplay of donor and acceptor communication-mediating (COM) domains. In this study, the potential of COM domains was exploited in vivo by establishing a system for the true biocombinatorial synthesis of lipopeptides via directed reprogramming of a natural NRP biosynthetic assembly line (i.e., surfactin). By means of COM domain swapping, these experiments verified the decisive role of COM domains for the control of protein-protein interactions between NRPSs, demonstrated the functionality of COM domain pairs even in the context of a heterologous host and NRPS system, and allowed for the intended skipping of a biosynthetic enzyme within a multienzymatic biosynthetic complex. Ultimately, abrogation of the selectivity barrier provided by COM domains afforded the successful simultaneous, biocombinatorial synthesis of distinct lipopeptide products.

Isolation of high molecular weight DNA fragments from soil, in excess of 1 Mb, and of sufficient quality for cloning into an Escherichia coli^streptomycete artificial chromosome vector is described. The combination of indirect extraction of cells, using a nycodenz extraction technique, followed by lysis of biomass immobilised in agarose plugs, allowed fragments in excess of 1 Mb to be purified.