title: DNA recognition by the DNA primase of bacteriophage T7: a structure-function study of the zinc-binding domain.
abstract: Synthesis of oligoribonucleotide primers for lagging-strand DNA synthesis in the DNA replication system of bacteriophage T7 is catalyzed by the primase domain of the gene 4 helicase-primase. The primase consists of a zinc-binding domain (ZBD) and an RNA polymerase (RPD) domain. The ZBD is responsible for recognition of a specific sequence in the ssDNA template whereas catalytic activity resides in the RPD. The ZBD contains a zinc ion coordinated with four cysteine residues. We have examined the ligation state of the zinc ion by X-ray absorption spectroscopy and biochemical analysis of genetically altered primases. The ZBD of primase engaged in catalysis exhibits considerable asymmetry in coordination to zinc, as evidenced by a gradual increase in electron density of the zinc together with elongation of the zinc-sulfur bonds. Both wild-type primase and primase reconstituted from purified ZBD and RPD have a similar electronic change in the level of the zinc ion as well as the configuration of the ZBD. Single amino acid replacements in the ZBD (H33A and C36S) result in the loss of both zinc binding and its structural integrity. Thus the zinc in the ZBD may act as a charge modulation indicator for the surrounding sulfur atoms necessary for recognition of specific DNA sequences.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: Barak
authors.initials: B
authors.lastname: Akabayov
authors.forename: Seung-Joo
authors.initials: SJ
authors.lastname: Lee
authors.forename: Sabine R
authors.initials: SR
authors.lastname: Akabayov
authors.forename: Sandeep
authors.initials: S
authors.lastname: Rekhi
authors.forename: Bin
authors.initials: B
authors.lastname: Zhu
authors.forename: Charles C
authors.initials: CC
authors.lastname: Richardson
mesh_terms: D019943:Amino Acid Substitution / Q000187:drug effects / Q000235:genetics; D017123:Bacteriophage T7 / Q000187:drug effects / Q000201:enzymology*; D055162:Biocatalysis / Q000187:drug effects; D002712:Chlorides / Q000494:pharmacology; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000378:metabolism; D019915:DNA Primase / Q000737:chemistry* / Q000378:metabolism*; D004279:DNA, Viral / Q000378:metabolism*; D004795:Enzyme Stability / Q000187:drug effects; D006639:Histidine / Q000378:metabolism; D008024:Ligands; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D009843:Oligoribonucleotides / Q000096:biosynthesis; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D013698:Templates, Genetic; D056928:X-Ray Absorption Spectroscopy; D015032:Zinc / Q000378:metabolism*; D017967:Zinc Compounds / Q000494:pharmacology
chemical_list: D002712:Chlorides; D004279:DNA, Viral; D008024:Ligands; D050505:Mutant Proteins; D009843:Oligoribonucleotides; D017967:Zinc Compounds; D006639:Histidine; C016837:zinc chloride; D019915:DNA Primase; D015032:Zinc; D003545:Cysteine