A core enzyme consists of the subunits of an enzyme that are needed for catalytic activity, as in the core enzyme RNA polymerase.

An example of a core enzyme is a RNA

RNA

Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....

 polymerase

Polymerase

A polymerase is an enzyme whose central function is associated with polymers of nucleic acids such as RNA and DNA.The primary function of a polymerase is the polymerization of new DNA or RNA against an existing DNA or RNA template in the processes of replication and transcription...

 enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 without the sigma factor

Sigma factor

A sigma factor is a bacterial transcription initiation factor that enables specific binding of RNA polymerase to gene promoters. Different sigma factors are activated in response to different environmental conditions...

 (σ). This enzyme consists of only two alpha (2α), one beta (β) and one beta prime (β'). This is just one example of a core enzyme. DNA Pol I can also be characterized as having core and holoenzyme segments, where the 5'exonuclease can be removed without destroying enzyme functionality.