<P> Nuclear actin exists mainly as a monomer, but can also form dynamic oligomers and short polymers . Nuclear actin organization varies in different cell types . For example, in Xenopus oocytes (with higher nuclear actin level in comparison to somatic cells) actin forms filaments, which stabilize nucleus architecture . These filaments can be observed under the microscope thanks to fluorophore - conjugated phalloidin staining . </P> <P> In somatic cell nucleus however we cannot observe any actin filaments using this technique . The DNase I inhibition assay, so far the only test which allows the quantification of the polymerized actin directly in biological samples, have revealed that endogenous nuclear actin occurs indeed mainly in a monomeric form . </P> <P> Precisely controlled level of actin in the cell nucleus, lower than in the cytoplasm, prevents the formation of filaments . The polymerization is also reduced by the limited access to actin monomers, which are bound in complexes with ABPs, mainly cofilin . </P> <P> Little attention is paid to actin isoforms, however it has been shown that different isoforms of actin are present in the cell nucleus . Actin isoforms, despite of their high sequence similarity, have different biochemical properties such as polymerization and depolymerization kinetic . They also shows different localization and functions . </P>

Where is the protein called actin located in the body