Browsing by Subject "actin-related protein"

Actin is known as abundant cytoplasmic protein, which functions as a component of the cytoskeleton and in cell motility together with motor protein myosins. However, actin is also present in the nucleus, where it has been shown to take part in the control of gene expression, both independently and as part of chromatin remodeling complexes. An important aspect in the study of nuclear actin is to identify other nuclear proteins interacting with actin and to confirm these interactions in biochemical experiments. Through these interactions actin can be linked to various nuclear processes. The aim of this master’s thesis study was to express and purify five nuclear proteins that have been suggested to bind actin and to study the binding in detail both with actin filaments and monomers. The proteins of interest include four actin-related proteins (ARPs) Arp4, Arp5, Arp6 and Arp8 as well as RNA polymerase II subunit Rpb8. Out of the proteins selected for this study, the expression and purification of Arp4 and Rpb8 was successful. Neither one did bind monomeric actin with high affinity, but interestingly Rpb8 did bind actin filaments. On the other hand, Rpb8 did not have any effect on actin polymerization. These results provide new insights into nuclear actin function. It has been suggested earlier that Arp4 would form a heterocomplex with actin, but the results of this study do not support this. The binding between Rpb8 and actin in RNA polymerase II complex has not been extensively studied before, so the results provide new information about the function of actin in the polymerase complex.