The present invention provides an isolated peptide of SEQ ID NO: 1 needed for primase active as well as new replicative DNA polymerase enzymes, preferably that of SEQ ID NO: 2, comprising said peptide. Thus, these DNA polymerases are endowed with priming activity and do not require externally provided primers for initiating and performing DNA amplification. These polymerases are able to carry out a faithful and processive de novo DNA synthesis of DNA templates in the absence of pre-synthetized primers. Therefore, these enzymes of the invention act both as primases and DNA polymerases. Furthermore, they show translesion synthesis capacity, so that they may be useful not only for whole-genome amplification but also for the amplification of damaged DNAs. The invention further refers to methods for amplifying templates DNAs using these enzymes.