The Essential Role of the 39 Terminal Template Base in the First Steps of Protein-Primed DNA Replication

Bacteriophages w29 and Nf from Bacillus subtilis start replication of their linear genomes at both ends using a protein-primed mechanism by means of which the DNA polymerase initiates replication by adding dAMP to the terminal protein, this insertion being directed by the second and third 39 terminal thymine of the template strand, respectively. In this work, we have obtained evidences about the role of the 39 terminal base during the initiation steps of w29 and Nf genome replication. The results indicate that the absence of the 39 terminal base modifies the initiation position carried out by w29 DNA polymerase in such a way that now the third position of the template, instead of the second one, guides the incorporation of the initiating nucleotide. In the case of Nf, although the lack of the 39 terminal base has no effect on the initiation position, its absence impairs further elongation of the TP-dAMP initiation product. The results show the essential role of the 39 terminal base in guaranteeing the correct positioning of replication origins at the polymerization active site t