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. Author manuscript; available in PMC: 2019 Dec 1.
Published in final edited form as: Curr Opin Struct Biol. 2018 Sep 12;53:131–139. doi: 10.1016/j.sbi.2018.08.003

Fig. 4.

Fig. 4

Comparison of loaders of ring-shaped proteins from bacteriophage T4 and S. cerevisiae.

(a) Schematic of the T4 DNA polymerase clamp loader (gp44 and gp62) bound to the gp45 clamp [an analogue of the eukaryotic PCNA]. (b) Surface representation of the structure of the T4 clamp loader bound to the clamp. (c) Cartoon representation of gp44 subunits A,B,C bound to primer-template DNA (red and blue strands) (d) Schematic of the S. cerevisiae helicase loader (ScORC+Cdc6) and pre-helicase complex (MCM+Cdt1). (e) Surface representation of the structure of ScOrc-Cdc6 bound to the MCM complex and Cdt1 on double strand origin DNA (f) Cartoon representation of ScORC subunits 1,4,5 bound to double-stranded DNA [red and blue strands]. (c) and (f) illustrate the corkscrew orientation of the subunits in the clamp loader and in ORC, both of which surround dsDNA.