Sequence Variations in the Non-Coding Sequence of CTX Phages in Vibrio cholerae.

This study focused on the variations in the non-coding sequences between ctxB and rstR of various CTX phages. The non-coding sequences of CTX-1 and CTX-cla are phage type-specific. The length of the non-coding region of CTX-1 and CTX-cla is 601 and 730 nucleotides, respectively. The non-coding sequence of CTX phage could be divided into three regions. There is a phage type-specific Variable region between two homologous Common regions (Common regions 1 and 2). The non-coding sequence of RS1 element is similar to CTX-1 except that Common region 1 is replaced by a short RS1-specific sequence. The non-coding sequences of CTX-2 and CTX-cla are homologous, indicating the non-coding sequence of CTX-2 is derived from CTX-cla. The non-coding region of CTX-O139 is similar to CTX-cla and CTX-2; however, it contains an extra phage type-specific sequence between Common region 2 and rstR. The variations in the non-coding sequences of CTX phages might be associated with the difference in the replication efficiency and the directionality in the integration into the V. cholerae chromosome.