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J. Bacteriol., Aug 1995, 4333-4341, Vol 177, No. 15
G Ziegelin, NA Linderoth, R Calendar and E Lanka
Bacteriophage P4 DNA replication depends on the product of the alpha gene,
which has origin recognition ability, DNA helicase activity, and DNA
primase activity. One temperature-sensitive and four amber mutations that
eliminate DNA replication in vivo were sequenced and located in the alpha
gene. Sequence analysis of the entire gene predicted a domain structure for
the alpha polypeptide chain (777 amino acid residues, M(r) 84,900), with
the N terminus providing the catalytic activity for the primase and the
middle part providing that for the helicase/nucleoside triphosphatase. This
model was confirmed experimentally in vivo and in vitro. In addition, the
ori DNA recognition ability was found to be associated with the C-terminal
third of the alpha polypeptide chain. The type A nucleotide-binding site is
required for P4 replication in vivo, as shown for alpha mutations at G-506
and K-507. In the absence of an active DnaG protein, the primase function
is also essential for P4 replication. Primase-null and helicase-null
mutants retain the two remaining activities functionally in vitro and in
vivo. The latter was demonstrated by trans complementation studies,
indicating the assembly of active P4 replisomes by a primase-null and a
helicase-null mutant.
Copyright © 1995, American Society for Microbiology
Domain structure of phage P4 alpha protein deduced by mutational analysis
Max-Planck-Institut fur Molekulare Genetik, Berlin, Germany.
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