The LSm proteins are known to organize as multiprotein ring assemblies which interact with RNAs to allow chemical modification or nuclease protection. The determination of structures of large heterogenous protein complexes poses particular difficulty for structural biologists, requiring the careful assembly of components into a viable complex suitable for data collection. Avenues for in vitro assembly include recombinant construction of all or some components via co expression, or expression of polyproteins with engineered linkers. We describe our polyprotein construction of appropriate dimer, trimer and heptamer combinations known to make up mixed LSm subcomplexes. By reconstituting mixed complexes of LSms we are defining the heteroheptameric ring assemblies by crystallography and studying their specific interactions their associated protein factors.