To better understand the functionality of T4 DNA replication, in depth structural analysis will require complexes between proteins and DNA substrates. The structures of T4 gp41 helicase, gp61 primase, and T4 DNA ligase are unknown, structures from bacteriophage T7 proteins are discussed instead. The T4 gp44/62 clamp loader has not been crystallized but a comparison to the E. The core of T4 gp32 and two proteins from the T4 related phage RB69, the gp43 polymerase and the gp45 clamp are also solved. Three of the ten full-length T4 replisomal proteins have been determined the gp59 helicase loading protein, the RNase H, and the gp45 processivity clamp. In this review, we discuss the structures that are available and provide comparison to related proteins when the T4 structures are unavailable.
As a consequence, significant effort has been put forth to solve the crystallographic structures of these replisomal proteins. The T4 provides a model system for DNA replication. The RNaseH, a 5' to 3' exonuclease and T4 DNA ligase comprise the activities necessary for Okazaki repair. The primosomal proteins include the gp41 hexameric helicase, the gp61 primase, and the gp59 helicase loading protein. The replicase includes the gp43 DNA polymerase, the gp45 processivity clamp, the gp44/62 clamp loader complex, and the gp32 single-stranded DNA binding protein. The replisomal proteins can be subdivided into three activities the replicase, responsible for duplicating DNA, the primosomal proteins, responsible for unwinding and Okazaki fragment initiation, and the Okazaki repair proteins. The bacteriophage T4 encodes 10 proteins, known collectively as the replisome, that are responsible for the replication of the phage genome.
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