Abstract
Tandem repeat proteins (TRPs) are a widespread class of non-globular proteins that contain repetitive stretches of amino acids. Structured tandem repeats in proteins (STRiPs) are a specific type of tandem repeats, characterized by a modular three-dimensional structure arrangement. The majority of STRiPs adopt solenoidal structures, but with the increased availability of experimental structural data and top-quality structural predictive models more STRiPs folds can be characterized. Here, we describe an overlooked STRiPs fold present in the DNA sliding clamp processivity factors, which has eluded classification although structural data has been available since the late 1990s. "Box" repeats comprise a fold inside class V of "beads-on-a-string" STRiPs which has been added to the RepeatsDB database, which now provides structural annotation for 66 of these proteins belonging to different organisms, including viruses.