The mini-derivatives were constructed by cloning DNA fragments containing the plasmid maintenance modules (including plasmid replication initiation modules), into the E. coli-specific, mobilizable, narrow-host-range vector pABW1 (ColE1-type ori of pMB1) [ 55].
These polyketides are synthesized by bimodular PKSs comprising of a dedicated initiation module, which includes a ketosynthase, acyl transferase and ACP, as well as a minimal PKS module.
Recently we showed that regioselectively modified polyketides could be synthesized through the genetic recombination of initiation modules and minimal PKS modules from different polyketide biosynthetic pathways (Tang et al. PLoS Biol. 2004, 2, 227 238).
For example, the actinorhodin and tetracenomycin minimal PKSs could accept and elongate unnatural primer units from the R1128 initiation module.
Nine subdomains encoding diverse specificities were transplanted into the Phe-specific GrsA initiation module of gramicidin S synthetase.
These results demonstrate that our replication initiation module is a functional replacement for the corresponding black box in Chen's whole cell cycle model.
In all figures we have color coded the nodes according the module: blue for initiation, yellow for ectoderm, gray for mesoderm, brown for mixed, and green for other.
It is unclear if these gene clusters are incomplete (missing an initiation module) or if these gene clusters encode an NRPS natural product.
Three NRPS gene clusters (Cluster 1 3) were identified from four Subsection V cyanobacterial genomes which lack a C domain in the initiation module.
In the initiation module, ACP is activated, condensed with malonyl CoA (using Malonyl-CoA ACP transacylase, FabD) and undergoes the first condensation reaction via β-Ketoacyl-ACP Synthase III (FabH).
The remaining 10 gene clusters which likely encode a NRPS/PKS natural product all encode an initiation module containing an AS domain which likely selects for a fatty acid molecule as the starter unit for biosynthesis, such as those observed in the jam, hct and hap gene clusters.
