:

   SATELLITE SEQUENCES
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     Long arrays of highly repeated simple oligonucleotide
   sequences with characteristic buoyant densities on cesium
   chloride gradients performed either with or without the action
   of DNA-binding antibiotics or metal ions.  Comprise approxi-
   mately 20% of the Drosophila melanogaster DNA complement.
   Confined to, and comprise the majority of, the pericentric
   heterochromatin of all chromosomes in the complement.  Four
   satellite peaks in cesium chloride gradients can be separated
   from the main band, which contains the euchromatic DNA
   (Peacock, Brutlag, Goldring, Appels, Hinton, and Lindsley,
   1973, Cold Spring Harbor Symp. Quant. Biol. 38:  405-16).
   These sequences do not become amplified in polytene chromo-
   somes and remain at the diploid-cell concentration (Gell,
   Cohen, and Polan, 1971, Chromosoma 33:  319-44).  Large clones
   of 1.672, 1.686, and 1.705 g/ml satellite DNA sequences in E.
   coli are unstable, but segments of 300 to 600 base pairs can
   be stably cloned in pBR322; it is found that samples of such
   clones derived from a single peak of the gradient may contain
   one major and several minor repeating sequences (Lohe and
   Brutlag, 1986, Proc. Nat. Acad. Sci. USA 83: 696-700).

   buoyant          sequence        density        fraction of
   density (g/ml)   5  -> 3  (      class (g/ml)   total DNA (%)
   _____________________________________________________________

   1.663            (AACAA)n        1.672          0.06
   1.669            (AATAAAC)n      1.672          0.23
   1.672            (AATAT)n        1.672          3.1
   1.680            (AATAC)n        1.672          0.52
                                    1.686
   1.686            (AATAACATAG)n   1.686          2.1
   1.688            (359 bp)n       1.688          5.1
   1.688            (AATAGAC)n      1.686          0.24
   1.689, 1.701     (AAGAC)n        1.686          2.4
   1.693            (AATAG)n        1.686          0.23
                    (GAGAG)n
   1.705            (AAGAG)n        1.705          5.6

   (
     designated according to the sequence of the purine-rich
     strand.

     The five-, seven-, and ten-base-pair repeats in such clones
   of either major or minor satellite sequences are quite homo-
   geneous, displaying zero, one, or at most two deviant repeat
   units in stretches of approximately fifty such units (approxi-
   mately one base pair per kilobase).  The sequences are not
   random, but conform to the pattern (RRN)m(RN)n, where R
   represents a purine (usually A) and N represents C, T, or G.
   The 1.688 g/ml satellite is complex, consisting of a 359-
   base-pair repeating unit.  This sequence is quite variable
   among repeat units at about a dozen sites, but is otherwise
   highly conserved (Hsieh and Brutlag, 1979, J. Mol. Biol.
   135:  465-81).  Hsieh and Brutlag (1979, Proc. Nat. Acad. Sci.
   USA 76: 731-35) identified and partially purified a protein
   that binds specifically to the 1.688 g/ml satellite sequence.
   In situ hybridization of satellite sequences to polytene-
   chromosome preparation show labeling of the chromocenter, and
   (some at lower stringency) of a few euchromatic bands [e.g. 3C
   (359 bp), 7F (AATAC), 21D (AAGAG), telomeres (AAGAG) (Lohe and
   Roberts, 1988, Heterochromatin:  Molecular and structural
   aspects (R.S. Verma, ed.). Cambridge University Press, Cam-
   bridge, pp.  148-86].  Hybridization of radio labeled RNA
   transcribed from DNA of the different buoyant-density classes
   to mitotic chromosomes reveals the presence of homologous
   sequences in the pericentric heterochromatin (Steffensen,
   Appels, and Peacock, 1981, Chromosoma 82: 525-41).  1.672 g/ml
   DNA sequences are detected at the tip and in the middle of YL,
   and in the heterochromatin of chromosome 4 and to a lesser
   extent at the tip of YS and in the centromere regions of chro-
   mosomes 2 and 3.  1.705 g/ml sequences are detected in sub-
   stantial quantities at the tip and base of YL, the base of YS,
   and in the pericentric heterochromatin of both 2L and 2R and
   in lesser amounts at the tip of YS, the centromere region of
   the X, near the heterochromatic-euchromatic junction of 3R,
   and in the right arm of chromosome 4.  The 1.688 g/ml satel-
   lite is mostly localized to two blocks in the X heterochroma-
   tin, one near the middle in the vicinity of the nucleolus
   organizer and the other adjacent to the centromere and in a
   third block near the center of YL; it is also detected in
   order-of-magnitude lower amounts at the tip and base of YL,
   the nucleolus organizing region of YS, at the base of one arm
   each of chromosomes 2 and 3, and on the short arm of chromo-
   some 4 (Peacock, Lohe, Gerlach, Dunsmuir, Dennis, and Appels,
   1977, Cold Spring Harbor Symp. Quant. Biol. 42:  1121-35).