We recently reported that circular RNA is efficiently translated by a rolling circle amplification (RCA) mechanism in a cell-free Escherichia coli translation system. Recent studies have shown that circular RNAs composed of exonic sequences are abundant in human cells. However, whether these circular RNAs can be translated into proteins within cells remains unclear. In this study, we prepared circular RNAs with an infinite open reading frame and tested their translation in eukaryotic systems. Circular RNAs were translated into long proteins in rabbit reticulocyte lysate in the absence of any particular element for internal ribosome entry, a poly-A tail, or a cap structure. The translation systems in eukaryote can accept much simpler RNA as a template for protein synthesis by cyclisation. Here, we demonstrated that the circular RNA is efficiently translated in living human cells to produce abundant protein product by RCA mechanism. These findings suggest that translation of exonic circular RNAs present in human cells is more probable than previously thought.

Immobilization of biosignal molecules including growth factors and cytokines is important for developing biologically active materials which can contribute to tissue engineering as a component. The immobilization has more meanings than only immobilization of the enzyme in a bioreactor or ligand–receptor interactions, because the immobilized biosignal molecules work on cells which have very complex structures and functions. This review discusses recent progress in immobilization of biosignal molecules, including the mechanisms and design concepts.