ANALYSIS OF GC-RICH REPETITIVE NUCLEOTIDE-SEQUENCES IN GREAT APES

The genomes of four primate species, belonging to the families Pongida e (chimpanzee, gorilla, and orangutan) and Hylobatidae (gibbons), have been analyzed for the presence and organization of two human GC-rich heterochromatic repetitive sequences: beta Satellite (beta Sat) and Lo ngSau (LSau) repeats. By Southern blot hybridization and PCR, both fam ilies of repeats were detected in all the analyzed species, thus indic ating their origin in an ape ancestor. In the chimpanzee and gorilla, as in man, beta Sat sequences showed a 68-bp Sau3A periodicity and wer e preferentially organized in large clusters, whereas in the orangutan , they were organized in DNA fragments of 550 bp, which did not seem t o be characterized by a tandem organization. On the contrary, in each of the analyzed species, the bulk of LSau sequences showed a longer Sa u3A periodicity than that observed in man (450-550 bp). Furthermore, o nly in the chimpanzee genome some of LSau repeats seemed to be intersp ersed within blocks of beta Sat sequences. This sequence organization, which also characterizes the human genome, is probably absent in the gorilla. In fact, the analysis of a gorilla genomic library suggested that LSau repeats are not preferentially in linkage with beta Sat sequ ences. Moreover, LSau sequences were found in a genomic sector charact erized by the simultaneous presence of L1 and (CA) repeats, as well as of anonymous sequences and known genes. In spite of the different seq uence organization, the nucleotide differences between complete human and gorilla LSau repeats were very few, whereas one gorilla LSau repea t, interrupted by a probably-truncated L1 transposon, showed a higher degree of divergence. Besides the gorilla, this unusual sequence organ ization was detected in man, and, to a lesser extent, in the chimpanze e.