Plastid genome random walks

A common genome composition pattern in eubacteria is an asymmetry between
the leading and lagging strands resulting in opposite skew patterns in the
two replichores that lie between the origin and terminus of replication.
Although this pattern has been reported for a couple of isolated plastid
genomes, it is not clear how widespread it is overall in this chromosome.
Using a random walk approach, we examine plastid genomes outside of the
land plants, which are excluded since they are known not to initiate
replication at a single site, for such a pattern of asymmetry. Although it
is not a common feature, we find that it is detectable in the plastid
genome of species from several diverse lineages. The euglenozoa in
particular show a strong skew pattern as do several rhodophytes. There is
a weaker pattern in some chlorophytes but it is not apparent in other
lineages. The ramifications of this for analyses of plastid evolution are
discussed. This dataset contains the random walk plots for the genomes
analyzed.