Roles of bacteriophage T7 gene 4 proteins in providing primase and helicase functions in vivo.
The helicase and primase activities of bacteriophage T7 are distributed between the 56- and 63-kDa gene 4 proteins. The 56-kDa gene 4 protein lacks 63 amino acids found at the N terminus of the colinear 63-kDa protein and catalyzes helicase activity. The 63-kDa gene 4 protein catalyzes both primase and helicase activities. A bacteriophage deleted for gene 4, T7 delta 4-1, has been tested for growth by complementation on Escherichia coli strains that contain plasmids expressing either one or both of the gene 4 proteins. T7 delta 4-1 cannot grow (efficiency of plating, 10(-7)) on E. coli cells that express only 56-kDa gene 4 protein. In contrast, T7 delta 4-1 has an efficiency of plating of 0.1 on an E. coli strain that expresses only 63-kDa gene 4 protein in which glycine is substituted for methionine at position 64. A bacteriophage, T7 4B-, in which methionine at residue 64 is replaced by glycine, expresses only 63-kDa gene 4 protein. The burst sizes, latency periods, and Okazaki fragment sizes of T7 4B- are similar in the presence and absence of the 56-kDa gene 4 protein; however, T7 4B- has a reduced rate of DNA synthesis when compared with a phage that synthesizes both gene 4 proteins.
Mendelman
L V
LV
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115.
Notarnicola
S M
SM
Richardson
C C
CC
D000595:Amino Acid Sequence; D017123:Bacteriophage T7 / Q000201:enzymology* / Q000235:genetics*; D001483:Base Sequence; D004265:DNA Helicases / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D019915:DNA Primase; D004261:DNA Replication; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D005814:Genes, Viral; D007700:Kinetics; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides; D012316:RNA Nucleotidyltransferases / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D013045:Species Specificity; D013997:Time Factors
D009838:Oligodeoxyribonucleotides; D019915:DNA Primase; D012316:RNA Nucleotidyltransferases; D004265:DNA Helicases