The genomes of Old-World, New-World, and prosimian primates contain members of a large class of highly repetitive DNAs that are related to one another and to component alpha DNA of the African green monkey by their sequence homologies and restriction site periodicities. The members of this class of highly repetitive DNAs are termed the alphoid DNAs, after the prototypical member, component alpha of the African green monkey which was the first such DNA to be identified (Maio, 1971) and sequenced (Rosenberg et al., 1978). The alphoid DNAs appear to be uniquely primate sequences.--From the restriction enzyme cleavage patterns and Southern blot hybridizations under different stringency conditions, the alphoid DNAs comprise multiple sequence families exhibiting varying degrees of homology to component alpha DNA. They also share common elements in their restriction site periodicities (172 . n base-pairs), in the long-range organization of their repeating units, and in their banding behavior in CsCl and Cs2SO4 bouyant density gradients, in which they band within the bulk DNA as cryptic repetitive components.--In the three species from the Family Cercopithecidae examined, the alphoid DNAs represent the most abundant, tandemly repetitive sequence components, comprising about 24% of the African green monkey genome and 8 to 10% of the Rhesus monkey and baboon genomes. In restriction digests, the bulk of the alphoid DNAs among the Cercopithecidae appeared quantitatively reduced to a simple series of arithmetic segments based on a 172 base-pair (bp) repeat. In contrast with these simple restriction patterns, complex patterns were observed when human alphoid DNAs were cleaved with restriction enzymes. Detailed analysis revealed that the human genome contains multiple alphoid sequence families which differ from one another both in their repeat sequence organization and in their degree of homology to the African green monkey component alpha DNA.--The finding of alphoid sequences in other Old-World primate families, in a New-World monkey, and in a prosimian primate attests to the antiquity of these sequences in primate evolution and to the sequence conservatism of a large class of mammalian highly repetitive DNA. In addition, the relative conservatism exhibited by these sequences may distinguish the alphoid DNAs from more recently evolved highly repetitive components and satellite DNAs which have a more restricted taxonomical distribution.

KpnI restriction of DNAs from all anthropoid primates studied releases a conspicuous series of segments representing families of long, interspersed repetitive DNAs termed here the KpnI 1.2, 1.5, 1.8 and 1.9 kb families. Human KpnI 1.2 to 1.9 kb segments representative of these families were isolated and separately cloned in the KpnI site of a plasmid pBK5, specially constructed for this purpose. The KpnI clones did not cross-hybridize with cloned, primate alphoid sequences, suggesting that the KpnI families represent sequences separate and distinct from the alphoid DNAs. Secondary restriction analyses of cloned KpnI segments demonstrated microheterogeneity among individual members within the same KpnI family. Autoradiograms of capuchin monkey, AGM and human DNA cleaved with HaeIII, AluI or RsaI and hybridized to various cloned human KpnI sequences demonstrated a remarkable conservatism and relative simplicity in the organization of the KpnI families in the genomes of these widely divergent primates. The KpnI 1.2 kb and 1.5 kb families occur in high frequency (15%) among all plaques in two recombinant human genome libraries. Evidence is presented suggesting that the bulk of the KpnI families occur in the genome as clusters or congeries of higher molecular weight segments (greater than 2 kb) containing sequences homologous to the low molecular weight segments (1.2 to 1.9 kb).

The mammalian genome contains a variety of interspersed repetitive sequences of unknown function. It has, however, been suggested that interspersed repetitive sequences and their RNA transcripts are involved in the coordinate regulation of gene expression. Two major families of interspersed sequences in primates are the so-called Alu and KpnI families. Members of the KpnI families range in length from 1.2 to over 6 kilobases (kb). They exist in generally clustered arrangements, in 6 X 10(4) to 10(5) copies per diploid genome. Something is known of the arrangements of KpnI family sequences near human structural genes, but there has been no information on transcription of the sequences. We report here that the KpnI sequences are transcribed in HeLa cells by RNA polymerase II into abundant and heterogeneous species of RNA. The transcripts range in length from about 200 bases to over 5 kb, and are found predominantly in the non-polyadenylated fraction of the nuclear RNA. Transcripts homologous to both of the complementary strands of the KpnI sequences are present, but with a strong bias towards one strand.

Families of related, but nonidentical repetitive DNA sequences, termed the alphoid DNAs, have been identified and characterized in representative species from seven major primate Families. The sequences appear as old as the primate Order itself: they are found in a prosimian (lemur), in a New World monkey, and in all Old World primates examined, including man. The alphoid DNAs are uniquely primate sequences and they may represent the most abundant repetitive DNAs in the primate genome. - A classification scheme for two major families of alphoid DNAs is proposed that is based upon restriction enzyme analysis and Southern blotting with radioactive probes prepared from component alpha DNA (Maio, 1971) and from the human EcoRI dimer sequences (Manuelidis, 1976). The family of alphoid DNAs that hybridizes readily with component alpha is termed the HindIII family of alphoid DNAs. This family shows an almost universal distribution among present-day primates. The family of DNA sequences that hybridizes readily with the human EcoRI dimer probe is termed the EcoRI dimer family of alphoid DNAs. This family may be restricted to the great apes and man. The two probes permitted the discrimination of different, but related alphoid families in present-day primates. Multiple alphoid sequence families are found within the genomes of individual primates and the major primate taxa can be characterized by the representations of the various alphoid DNAs within their genomes. - An Appendix is presented (Brown et al., 1981) indicating that competition hybridization effects may influence the autoradiographic banding patterns, and hence, the interpretations of Southern filter-transfer hybridizations when dealing with related repetitive sequences such as the alphoid DNAs that are present in abundance in eukaryotic genomes.

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