Positive-strand RNA viruses associate with specific organelle membranes of host cells to establish viral replication complexes. The replication protein 1a of brome mosaic virus associates strongly with the nuclear endoplasmic reticulum (ER) membranes, invaginates membranes into the lumen, and recruits various host proteins to establish replication complexes termed spherules. 1a has a strong affinity towards the perinuclear ER membrane, however, the structural features in 1a that dictate its membrane associations and thereby membrane remodeling activities are unclear. This study examined the possible role of an amphipathic α-helix, helix B, in BMV 1a's membrane association. Deletion or single substitution of multiple amino acids of helix B abolished BMV 1a's localization to nuclear ER membranes. Additional reporter-based, gain-of-function assays showed that helix B is sufficient in targeting several soluble proteins to the nuclear ER membranes. Furthermore, we found that the helix B-mediated organelle targeting is a functionally conserved feature among positive-strand RNA viruses of the alphavirus-like superfamily that includes notable human viruses such as Hepatitis E virus and Rubella virus as well as plant viruses such as cucumber mosaic virus and cowpea chlorotic mottle virus. Our results demonstrate a critical role for helix B across members of the alphavirus-like superfamily in anchoring viral replication complexes to the organelle membranes. We anticipate our findings to be a starting point for the development of sophisticated models to use helix B as a novel target for the development of antivirals for positive-strand RNA viruses that belong to the alphavirus-like superfamily. / Doctor of Philosophy / Among the seven classes of viruses, the positive-strand RNA viruses dominate the domain of viral diseases of the world. Brome mosaic virus (BMV) is a positive-strand RNA virus that infects cereal crops such as wheat, barley, and rice. BMV has a simple genome organization and serves as a suitable model virus to study and characterize positive-strand RNA viruses. The replication of all positive-strand RNA viruses occurs at the organelle membranes of the host. Membrane association of the replication is one of the early steps and a crucial event in the life cycle of positive-strand RNA viruses. One of the proteins produced early on during BMV infection is the replication protein 1a, which is also the master regulator of viral replication; 1a recruits viral factors in addition to hijacking the necessary host factors at the membranous sites to initiate replication. Upon reaching the organelle membranes, 1a induces membrane rearrangements to form viral replication complexes that safeguard the recruited factors from the deleterious effects of the host cell. The structural determinants within 1a that are responsible for such membrane association are unknown. This study explored the potential roles of a short helical motif within the 1a protein for its ability to dictate such site-specific membrane associations. We show here that this helical region is necessary and sufficient for 1a's membrane-binding activity. We also discovered it to be a functionally conserved feature that is responsible for membrane associations in various viruses of the alphavirus-like superfamily that includes some of the notable human viruses such as Hepatitis E virus and Rubella virus in addition to plant viruses such as cucumber mosaic virus and cowpea chlorotic mottle virus.