This is the smallest and simplest of the classical eukaryotic polymerases; it is composed of a single
~40-48 kDa protein. Like most single polypeptide enzymes, Pol b is not highly active and is not
very processive. It has no intrinsic exonuclease activities. Its preferred template is duplex DNA
with short gaps, although it can bind a nicked duplex and is capable of some limited displacement
synthesis. Interestingly, however, it may also associate with PCNA.
Pol b expression is considered constitutive. Expression levels are low and remain constant
throughout the cell cycle, even in rapidly dividing cells. It is also expressed in quiescent cells.
However, Pol b levels increase following treatment of cells with agents that damage DNA.