Role of the potential secondary structures in phage g4 origin of complementary dna strand synthesis

Phage G4 origin of complementary DNA strand synthesis ( ori c) consists of three stable stem-loop structures (I, II, and III). Mutant ori c sequences with alterations in the structure of stem-loop II, stem-loop III, and the stem-loop II–III spacer region have been constructed and cloned into the filamentous phage vectors to assay their functional activity. Changes in the lowermost GC base pair in the stem of stem-loop III, in the 9-bp spacer region between the stems of stem-loops II and III, and in the loop of stem-loop II, impair or abolish in vivo ori c function. The results suggest that recognition sequences for dnaG primase must be present in the loop of stem-loop II, and in the spacer region between the stems of stem-loops II and III.