SkewDB: A comprehensive database of GC and 10 other skews for over 28,000 chromosomes and plasmids

GC skew denotes the relative excess of G nucleotides over C nucleotides on
the leading versus the lagging replication strand of eubacteria. While the
effect is small, typically around 2.5%, it is robust and pervasive. GC
skew and the analogous TA skew are a localized deviation from Chargaff’s
second parity rule, which states that G and C, and T and A occur with
(mostly) equal frequency even within a strand. Most bacteria also show the
analogous TA skew. Different phyla show different kinds of skew and
differing relations between TA and GC skew. This article introduces an
open access database (https://skewdb.org) of GC and 10 other skews for
over 28,000 chromosomes and plasmids. Further details like codon bias,
strand bias, strand lengths and taxonomic data are also included. The
SkewDB database can be used to generate or verify hypotheses. Since the
origins of both the second parity rule, as well as GC skew itself, are not
yet satisfactorily explained, such a database may enhance our
understanding of microbial DNA.