Architectural role of HMO1 in bending, bridging and compacting DNA

Abstract

HMO1 proteins are abundant Saccharomyces cerevisiae (yeast) High Mobility Group Box (HMGB) proteins. HMGB proteins are nuclear proteins which are known to have an architectural function. HMO1 possesses two HMGB box domains. It has been reported that double box HMGB proteins induce strong bends upon binding to DNA. It is also believed that they play an essential role in reorganizing chromatin and therefore are likely to be involved in gene activation. To characterize DNA binding we combine single molecule stretching experiments and AFM imaging of HMO1 proteins bound to DNA. By stretching DNA bound to HMO1, we determine the dissociation constant and measure protein induced average DNA bending angles. To further investigate the local nature of these bends, AFM images of HMO1-DNA complexes are imaged to probe the behavior of these complexes as a function of protein concentration. The results show that at lower concentrations, HMO1 preferentially binds to the ends of the double helix and links separate DNA strands. At higher concentrations HMO1 induces formation of a complex network that reorganizes DNA. Although HMG nuclear proteins are under intense investigation, little is known about HMO1. Our studies suggest that HMO1 proteins may facilitate interactions between multiple DNA molecules.