tokens: In contrast , in other ring - shaped DNA - binding proteins such as the beta subunit of E . coli DNA polymerase III ( 28 ) , gp45 of T4 DNA polymerase ( 29 ) , PCNA of eukaryotic DNA polymerases delta ( 30 , 31 ) and D . radiodurans RecR ( 27 ) , alpha - helices are located toward the center of the ring and are surrounded by beta - strands in the outermost side of the ring ( Figure 5 ) .