258
Anthology of Human Repetitive DNA
telomeric repeats can also be viewed as
satellite-like sequences. Because of their
distinct base composition, many satellites
were originally discovered as a result of
their separation from bulk DNA by cen-
trifugation in buoyant density gradients.
Satellites with GC content similar to that
of the unique genomic DNA, which could
not be separated by centrifugation, have
been called
cryptic satellites
.Thefunc
t
ion
of satellite DNA remains unclear. Satel-
lites represent up to 20% of the genomic
DNA, but they are underrepresented in the
sequenced portion of the genome.
Table 1 lists representative human satel-
lite sequences collected in Repbase Update
(RU), the reference collection of repetitive
sequences (Sect. 6.1). The most exten-
sively studied centromere- and telomere-
speciFc repeats are reviewed in the next
two sections. In addition, there are sev-
eral chromosome-speciFc tandem repeats,
some of which are listed in Table 1.
2.2.1
Centromeric Satellites
Human centromeric DNA contains a va-
riety of different satellite repeats. The
major noncryptic satellite fractions were
Tab. 1
Human satellites and satellite-like sequences in repbase update.
Repbase
Description
Centromeric
SAR
Satellite I
GAATG
Satellites II and III, both contain 5-ATTCC basic unit
HSATII
Satellite II (example, diverged copy)
ALR
Alpha satellite
ALR1
Alpha satellite subfamily 1
ALR2
Alpha satellite subfamily 2
BSR
Beta satellite
GSAT
Gamma satellite
GSATX
Gamma X satellite, X chromosome speciFc
CER
48-bp satellite
SN5
SN5 satellite
LSAU
Heterochromatic satellite
HSAT4
35-bp centromeric repeat
HSAT5
Centromeric repeat, 14-bp unit
GSATII
Centromere-associated repeat
D20S16
Centromere-associated repeat
Telomeric
TAR1
Telomere-associated repeat sequence, TAR1 or SUBTEL
sat in RepeatMasker
REP522
Repetitive subtelomeric-like sequence
Others
SATR1
Primate satellite-like sequence
SATR2
Primate satellite-like sequence
MSR1
37 bp minisatellite repeats, speciFc to chromosome 19, but detected in
chromosome 19-derived segmental duplications located in other chromosomes
MER22
SSTI moderately repetitive family, strictly tandem repeat, appearing at 2
chromosomal locations only
ACRO1
Satellite/acromeric in all short arms of acromeric chromosomes
HSATI
Chromosome 22 satellite
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