Initiation of DNA replication on single-stranded DNA templates catalyzed by purified replication proteins of bacteriophage lambda and Escherichia coli.

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Abstract
Initiation of bacteriophage .lambda. DNA replication at the chromosomal origin depends on the .lambda. O and P replication proteins. These 2 viral initiators, together with an E. coli protein fraction, promote the replication in vitro of single-stranded circular DNA chromosomes such as that of bacteriophage M13. This nonspecific strand initiation reaction, which was termed the .lambda. single-strand replication reaction, was now established with 8 purified proteins, each of which is also required for replication of the phage .lambda. chromosome in vivo. An early rate-limiting step in the overall reaction is the ATP-dependent assembly of an activated nucleoprotein prepriming complex. In this step the .lambda. O and P initiators cooperate with the E. coli dnaJ and dnaK proteins to transfer the bacterial dnaB protein onto M13 DNA that is coated with the single-stranded DNA protein. Multiple RNA primers are synthesized on each DNA circle when isolated prepriming complex is incubated with primase and ribonucleotriphosphates. In the complete system, DNA polymerase III holoenzyme extends the 1st primer synthesized into full-length complementary strands. Because the properties of this system are closely analogous to those found for the replication of .vphi.X174 viral DNA by E. coli proteins, it is inferred that a mobile prepriming or priming complex (primosome) operates in the .lambda. single-strand replication reaction.