Average AT contents of MITEs and their flanking sequences compared with
STS and EST sequences in the A. gambiae database. AT
contents of all full-length MITEs (see Table 1 for sample sizes) and
their flanking sequences (STS minus MITE, indicated by the suffix
“F”), and all of the 17,509 STS sequences in the A.
gambiae genome database were calculated. Calculations of the
Pegasus elements and their flanking regions were based
on sequences reported by Besansky et al. (22). The
forward and reverse sequences of the A. gambiae ESTs
were analyzed separately because many of them represent pairs of
sequences covering different regions of the same clone. Two hundred
ESTs were randomly selected from each of the 2,990 forward ESTs and the
2,936 reverse ESTs (27). They were analyzed by using blast
to remove redundancy that resulted from multiple copies of cDNAs. AT
contents of 186 nonredundant forward ESTs (EST-For) and 181
nonredundant reverse ESTs (EST-Rev) were calculated and analyzed. Data
points represent the mean AT contents. The error bar represents the
SEM. Note that the standard errors for several data points are too
small to be shown at the current scale. Mann–Whitney tests were used
to compare the medians at α = 0.05. In most cases,
t-tests were also used to compare the means, which gave
the same conclusions. Samples in tier I have significantly higher AT
contents than samples in tier II and III, whereas most samples in tier
II have significantly higher AT contents than samples in tier III. One
exception is TAA-I-AgF of tier II, which has a small
sample size. Its AT content is neither significantly higher than
samples in tier III nor significantly lower than
TA-Iα-AgF, TA-IIα-AgF,
TA-IV-AgF, and TA-IV-Ag of tier
I. The other exception is the comparison between
TAA-I-Ag and TA-IV-Ag, which is not
significantly different. Samples in tier II are not significantly
different from each other while EST-For is slightly more AT-rich than
EST-Rev in tier III (P = 0.045). A few samples in
tier I are slightly more AT-rich than others.