Gene 4 protein and DNA polymerase of bacteriophage T7 catalyze RNA-primed DNA synthesis on single-stranded DNA templates. T7 DNA polymerase exhibits an affinity for both gene 4 protein and single-stranded DNA, and gene 4 protein binds stably to single-stranded DNA in the presence of dTTP (Nakai, H. and Richardson, C. C. (1986) J. Biol. Chem. 261, 15208-15216). Gene 4 protein-T7 DNA polymerase-template complexes may be formed in both the presence and absence of nucleoside 5'-triphosphates. The protein-template complexes may be isolated free of unbound proteins and nucleotides by gel filtration and will catalyze RNA-primed DNA synthesis in the presence of ATP, CTP, and the four deoxynucleoside 5'-triphosphates. RNA-primed DNA synthesis may be dissected into separate reactions for primer synthesis and DNA synthesis. Upon incubation of gene 4 protein with single-stranded DNA, ATP, and CTP, a primer-template complex is formed; it is likely that gene 4 protein mediates stable binding of the oligonucleotide to the template. The complex, purified free of unbound proteins and nucleotides, supports DNA synthesis upon addition of DNA polymerase and deoxynucleoside 5'-triphosphates. Association of primers with the template is increased by the presence of dTTP or DNA polymerase during primer synthesis. DNA synthesis supported by primer-template complexes initiates predominantly at gene 4 recognition sequences, indicating that primers are bound to the template at these sites.