摘要：

There are many similarities in the replication mechanisms employed by bacteriophage λ and its host E. coli (for reviews, see Bramhill and Kornberg, 1988, Keppel et al., 1988, and McMacken et al., 1987). In both cases, the host-coded primase enzyme (the dnaG gene product) is mostly responsible for synthesizing the RNA primers for both the leading and lagging strand, to be extended into DNA by the DNA polymerase III holoenzyme. A major problem in both systems is that the primase enzyme is normally unable to make RNA primers by itself (except in the case of a few single-stranded bacteriophages). Instead, it must first make contact with the dnaB helicase, properly positioned on single-stranded DNA. The dnaB helicase unwinds DNA by traveling in the 5'→3' direction (LeBowitz and McMacken, 1986). To do so, the dnaB helicase must somehow "climb" onto DNA at a single-stranded region. Such a single-stranded DNA region is created at the E. coli oriC site by the binding of the dnaAATP protein form (Bramhill and Kornberg, 1988). To enter the single-stranded region at oriC , the dnaB helicase must be escorted by the dnaC initiation protein (Bramhill and Kornberg, 1988).

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