ABSTRACT
Mitochondrial gene rearrangements are much more frequent in vertebrates than initially thought. It has been suggested that the origin of light strand replication could have an important role in the process of gene rearrangements, but this hypothesis has never been tested before. We used amphibians to test the correlation between light-strand replication origin thermodynamic stability and the occurrence of gene rearrangements. The two variables were correlated in a non-phylogenetic approach, but when tested in a phylogenetically based comparative method the correlation was not significant, although species with unstable light-strand replication origins were much more likely to have undergone gene rearrangements. This indicates that within amphibians there are stable and unstable phylogenetic groups regarding mitochondrial gene order. The species analyzed showed variability in the thermodynamic stability of the secondary structure, in the length of its stem and loop, and several species did not present the 5-GCCGG-3 motif reported to be necessary for efficient mitochondrial DNA replication. Future studies should focus on the role of the light-strand replication origin in mitochondrial DNA replication and gene rearrangements mechanisms.
ABSTRACT
Starting from a naturally occurring cryptic plasmid pVC540 of Vibrio cholerae non-OI. strain 1095, a number of plasmid vectors have been constructed for cloning genes in Vibrio cholerae by introducing antibiotic resistance markers containing a set of unique cloning sites. The constructs pVC810 and pVE920 have the origins of both Vibrio cholerae and Escherichia coli replicons and are stable in both organisms in the absence of selective pressure. These plasmids can serve as shuttle vectors between Escherichia coli and Vibrio cholerae. The plasmid vectors reported here along with the demonstration of transformation in Vibrio cholerae by plasmid DNA will facilitate genetic analysis of this important human pathogen.