T4 codes for all the components of its own replication and recombination complexes, for an excision-repair enzyme, denV and for many enzymes that synthesize precursors for or modify T4 DNA. Some of the latter proteins (dCTPase, dCMP hydroxymethylase, deoxynucleotide kinase) specifically allow incorporation of HMC triphosphates during T4 DNA synthesis. The a and b DNA glucosylases sugar-coat the HMC-containing DNA after it has been polymerized, to protect it from attack by Mrc nucleases described above.
The basic replisome proteins of all organisms share sequence and structural similarities, and some of the T4 replication proteins can partially function in eukaryotic in vitro systems (307).
Initiation of T4 DNA replication is far more complex than structure and function of the basic replisomes. As we discuss in detail below, replication forks can be initiated in several different ways. There is necessary, but limited initiation from bonafide origins; most subsequent replication forks are initiated from intermediates of homologous recombination. There are several redundant origins of DNA replication, and there are several pathways of recombination-dependent DNA replication. We surmise that these redundant pathways are exquisitely suited to adjust DNA replication to different transcription patterns, described above, to environmental conditions and to packaging of DNA described below.
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