Minicircle

Minicircle refers to small circular DNA molecules that occur in two main contexts in biology and biotechnology. In genetic engineering, minicircle DNA vectors are compact circular DNA constructs derived from larger plasmids by removing bacterial backbone sequences. The resulting molecule contains only the gene of interest and essential regulatory elements such as a promoter and a polyadenylation signal. The absence of bacterial sequences reduces CpG motifs and overall immunogenicity, often allowing higher and more persistent transgene expression in mammalian cells. Minicircles are produced by recombination-based methods that excise the bacterial backbone, yielding a clean expression cassette suitable for purification. They are used for gene therapy, DNA vaccination, and research where robust and durable expression is desired. Typical minicircles range from about two to several kilobases in size, depending on the insert and regulatory elements.

In the biology of certain protozoa, minicircles are small circular DNA elements that form part of the kinetoplast DNA, the mitochondrial genome of many kinetoplastids such as Trypanosoma and Leishmania. These minicircles, together with larger maxicircles, constitute a densely interlocked network within the mitochondrion. Minicircles commonly encode guide RNAs that direct RNA editing required for expression of mitochondrial genes. The network contains thousands of minicircles, which are diverse in sequence and copy number and are maintained by specialized replication and segregation systems distinct from standard chromosomal replication.

Taken together, minicircles describe distinct but related genetic elements that share the characteristic of being small circular DNA molecules with different biological roles: as compact vectors for gene delivery and as natural mitochondrial DNA components in kinetoplastid parasites.