title: Insertion of an intermediate repetitive sequence into a sea urchin histone-gene spacer.
abstract: A common polymorphism of the early embryonic histone-gene repeat of Strongylocentrotus purpuratus is a 195-bp insertion within the H4-H2B spacer. The sequence, found as an insert in histone-gene repeats of 6 of 22 individuals screened, is also found at approximately 50 sites elsewhere in the genome of every individual. We compare the sequences of the histone-gene spacers that do and do not contain the insert. The insert is found not to have transposon-like features, and no sequence in the original spacer has been duplicated to flank the insert. There is, however, a hexanucleotide sequence that is repeated three times at one end of the insert, and the element has inserted between direct repeats of 5 bp that were present in the original spacer. One of the copies found outside the histone gene cluster was cloned and sequenced and is compared with the insert. Again, no transposon-like features are evident. Regions flanking the homologous sequence in this clone were used as hybridization probes in whole-genome blots. Results indicate that the 195-bp sequence insert is itself embedded within a larger element that is repeated within the genome. Therefore, only a portion of a larger repetitive sequence has integrated into the histone-gene spacer. The sequence features of the insert, although not typical of mobile elements, may be representative of other illegitimate recombination events.
mesh_terms: D000818:Animals; D001483:Base Sequence; D004262:DNA Restriction Enzymes; D004251:DNA Transposable Elements; D005796:Genes; D006657:Histones / Q000235:genetics*; D008297:Male; D011110:Polymorphism, Genetic; D012091:Repetitive Sequences, Nucleic Acid; D012617:Sea Urchins / Q000235:genetics*; D013094:Spermatozoa
chemical_list: D004251:DNA Transposable Elements; D006657:Histones; D004262:DNA Restriction Enzymes