DNA-POLYMERASE DELTA-DEPENDENT FORMATION OF A HAIRPIN STRUCTURE AT THE 5'-TERMINAL PALINDROME OF THE MINUTE IRUS OF MICE GENOME

The parvovirus the minute virus of mice (MVM) has a linear single-stra nded DNA genome with unique palindromic sequences at both termini whic h enable it to fold back on itself and form hairpin or cruciform-type structures. The purpose of this study was to examine the primary event s occurring during MVM replication mediated solely by the host cell re plication machinery. In an in vitro DNA replication system using HeLa cell extracts, we found that there was a distinct activity that utiliz ed the 5' terminal palindrome sequence of MVM to produce a secondary s tructure from a duplex extended form, in a time-dependent fashion. The secondary structure was due to the formation of a hairpin rather than a stem-plus-arms type structure and was associated with initiation of DNA synthesis, performed specifically by DNA polymerase delta. Inhibi tion of DNA polymerase cu had no effect upon this activity. Removal of all but 13 base pairs of the hairpin arm abolished the synthesis of D NA, indicating that there is a minimal length requirement for the dupl ex region of DNA or that this region contains regulatory genetic eleme nts. These data are consistent both with the role of DNA polymerase de lta in extending the synthesis of DNA from a DNA primer and with unidi rectional continuous DNA synthesis, initiating from a hairpin, as a mo de of replication for MVM. (C) 1996 Academic Press, Inc.