Christophe Possoz - Role of the Co-helicase DciA in DNA Replication in Vibrio cholerae

During bacterial DNA replication, replicative helicases separate the two DNA strands at the replication fork. In Escherichia coli, this process depends on the co-helicase DnaC, which is required for loading and activating the helicase DnaB. However, most bacteria possess another ancestral co-helicase called DciA. Unlike DnaC, DciA is not strictly required for DnaB loading, although it remains essential for cell survival. This study aimed to determine the precise role of DciA during replication initiation. Replication analyses revealed that in the absence of DciA, replication often becomes unidirectional, meaning that only one replication fork progresses efficiently. This abnormal process generates DNA double-strand ends, which are recognized by the repair protein RecB. RecB then promotes replication restart, allowing bidirectional replication to be restored. Without this repair mechanism, chromosome 1 of V. cholerae undergoes degradation. Our model proposes that DciA ensures the normal bidirectional initiation of DNA replication. However, the essential nature of DciA cannot be explained solely by its role in replication initiation. Even when unidirectional replication was artificially induced, cells remained viable. These findings suggest that DciA possesses another essential cellular function that still remains unknown.