ORANGUTAN ALPHA-SATELLITE MONOMERS ARE CLOSELY-RELATED TO THE HUMAN CONSENSUS SEQUENCE

Alpha-satellite is a family of tandemly repeated DNA found at the cent romeric regions of all human and primate chromosomes. Human alpha-sate llite subsets are largely chromosome-specific and have been further gr ouped into four suprachromosomal families (SFs), each characterized by a unique set of monomeric types. Although chimpanzee and gorilla alph a-satellites share sufficient sequence similarity to fit the establish ed SFs, the assumption that the derived human alpha-satellite consensu s and monomeric types represent the sequence of ancestral repeats rema ins unestablished. By using oligonucleotide primers specific for a con served region of human alpha-satellite DNA, we have PCR amplified, clo ned, and characterized alpha-satellite sequences from the orangutan ge nome. Nucleotide sequence analysis demonstrated that orangutan alpha-s atellite is formed by a single monomeric type that is sig nificantly c loser in percentage of sequence identity (mean = 92%, range = 89-96%) to the overall consensus of human alpha-satellite than to the monomeri c types corresponding to the four SFs. Use of cloned sequences as hybr idization probes to orangutan genomic DNA digested with a panel of res triction enzymes showed that most orangutan alpha-satellite subsets ar e characterized by a monomeric construction. The subset homologous to clone PPY2-5 is organized in distinct higher-order repeat structures c onsisting of 18 adjacent monomers. By FISH two clones, PPY3-4 and PPY3 -5, proved to be specific for the alpha-satellite on the orangutan hom ologs of human Chromosomes (Chrs) 10 and 8, respectively. Our data ind icate that there was an ancestral monomeric type displaying high seque nce similarity to the overall human consensus from which the different great ape and human subsets and SFs may have originated.