- pEC156 is a naturally occurring plasmid found in Escherichia coli, classified as a small, high-copy-number, non-conjugative but mobilizable plasmid. With an approximate size of 5.4 kilobases, pEC156 belongs to the ColE1 family of plasmids, which are characterized by their RNA-based replication control and high replication efficiency within host cells. The plasmid has been primarily studied for its role in plasmid mobilization and its utility in molecular biology as a genetic tool.
- Although pEC156 does not possess the full set of genes required for autonomous conjugation (such as the tra operon), it carries a functional mob region consisting of mobA and mobC genes. The mobA gene encodes a relaxase enzyme that initiates plasmid transfer by introducing a site-specific nick at the origin of transfer (oriT), while mobC is believed to assist in the proper functioning of the relaxosome complex. This genetic configuration allows pEC156 to be mobilized by conjugative plasmids that provide the necessary transfer machinery in trans, thus facilitating horizontal gene transfer among bacteria.
- The plasmid’s origin of replication is of the ColE1 type, which relies on the interaction between two small RNAs, RNA I and RNA II, to regulate plasmid copy number. This mechanism allows for stable inheritance and a relatively high copy number per cell, making pEC156 a suitable backbone for constructing recombinant plasmids in genetic engineering applications. Naturally, pEC156 does not encode antibiotic resistance genes; however, in laboratory variants or engineered derivatives, genes such as cat (conferring chloramphenicol resistance) have been inserted to enable selection.
- From a functional standpoint, pEC156 has been widely used in research focusing on the mechanics of plasmid mobilization and incompatibility. It serves as a model system to understand how small mobilizable plasmids interact with conjugative elements, how they are maintained within bacterial populations, and how they contribute to the broader ecology of plasmid-mediated gene transfer. Moreover, its compact size and well-defined features have made it a useful platform for the development of shuttle vectors and other synthetic constructs, especially in studies involving Gram-negative bacteria.
