Role of the RepA1 protein in RepFIC plasmid replication.

Using a sensitive primer extension technique, we have carried out studies to localize the start site of replication of the replicon RepFIC. In the course of these studies, we have found evidence that supports the hypothesis that transcription is an integral component of the initiation of replication. On the basis of our findings, we suggest that the transcript is processed to act as a primer, and therefore we propose that the transcript has a dual role as primer of replication and mRNA for the RepA1 protein. We present a model, based on our evidence, for the initiation of replication of the replicon RepFIC. This model provides as well an alternative explanation for what has been called the cis action of RepA1, and we show that RepA1 may act in trans as well as in cis.