title: The helicase domain of phage P4 alpha protein overlaps the specific DNA binding domain.
abstract: Replication initiation depends on origin recognition, helicase, and primase activities. In phage P4, a second DNA region, the cis replication region (crr), is also required for replication initiation. The multifunctional alpha protein of phage P4, which is essential for DNA replication, combines the three aforementioned activities on a single polypeptide chain. Protein domains responsible for the activities were identified by mutagenesis. We show that mutations of residues G506 and K507 are defective in vivo in phage propagation and in unwinding of a forked helicase substrate. This finding indicates that the proposed P loop is essential for helicase activity. Truncations of gene product alpha (gp alpha) demonstrated that 142 residues of the C terminus are sufficient for specifically binding ori and crr DNA. The minimal binding domain retains gp alpha's ability to induce loop formation between ori and crr. In vitro and in vivo analysis of short C-terminal truncations indicate that the C terminus is needed for helicase activity as well as for specific DNA binding.
authors.affiliation: Max-Planck-Institut für Molekulare Genetik, Berlin, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Ziegelin
authors.forename: R
authors.initials: R
authors.lastname: Calendar
authors.forename: R
authors.initials: R
authors.lastname: Lurz
authors.forename: E
authors.initials: E
authors.lastname: Lanka
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D003545:Cysteine / Q000378:metabolism; D004265:DNA Helicases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019915:DNA Primase; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D005998:Glycine; D006639:Histidine; D008239:Lysine; D009154:Mutation; D012316:RNA Nucleotidyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity; D013879:Thioredoxins / Q000378:metabolism; D014764:Viral Proteins
chemical_list: D004268:DNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D014764:Viral Proteins; C095083:alpha protein, Bacteriophage P4; D006639:Histidine; D013879:Thioredoxins; D019915:DNA Primase; D012316:RNA Nucleotidyltransferases; D000251:Adenosine Triphosphatases; D004265:DNA Helicases; D008239:Lysine; D003545:Cysteine; D005998:Glycine