We have analyzed and compared the responses of the three major HeLa cell DNA polymerases (alpha, beta, and gamma) to a HeLa DNA template with short RNA or DNA primers hybridized to it. Only DNA polymerase alpha is able to synthesize DNA covalently bonded to the RNA primer via a 3' yields 5' phosphodiester bond. 32P transfer experiments showed that all combinations of ribo- and deoxyribonucleotides are represented in the RNA-DNA linkages but their distribution is nonrandom. The RNA-DNA linked molecules base-paired to a HeLa DNA template strand represent a possible "natural" in vitro primer-template for DNA polymerases and can be extended by all three DNA polymerases (alpha, beta, and gamma). These findings indicate that DNA polymerases beta and gamma are capable of DNA-primed but not RNA-PRIMED DNA synthesis, while DNA polymerase alpha is capable of both RNA-primed and DAN-primed DNA synthesis.