Chromosomal assignments of genes coding for human leukocyte common antigen, T-200, and lymphocyte function-associated antigen 1, LFA-1 beta subunit

Five hybrids reactive with monoclonal antibodies against human leukocyte common antigen (T-200) and/or lymphocyte function-associated antigen 1 (LFA-1) beta subunit were obtained from the fusion of human blood lymphocytes or T-cell chronic lymphocytic leukemia cells with BW5147 mouse T-cell leukemia cells. Chromosome analyses of 20 clones showed concordance between the presence of human chromosomes 1 and 21 and the expression of T-200 and LFA-1 beta subunit, respectively. Confirmation of human chromosomes in the hybrids was made by the electrophoretic analyses of phosphoglucomutase for chromosome 1 and superoxide dismutase for chromosome 21. The results suggested that the presence of human chromosomes 1 and 21 was essential for the expression of T-200 and LFA-1 beta subunit, respectively.

Isolation of a human genomic fragment, co-amplified with c-Ki-ras, that affects plasmid supercoiling in E. coli

Amplification of cellular proto-oncogenes has been implicated in the development of human malignancies. A library was constructed from genomic DNA extracted from a lung tumour, previously shown to carry an amplified c-Ki-ras 2 gene. Using a v-Ki-ras probe, a fragment with ras homology was isolated and shown to be amplified in the original tumour DNA to the same level as c-Ki-ras. Studies with human hamster hybrids demonstrated that it is normally located on human chromosome 12 (as is c-Ki-ras). The restriction map of the fragment is different from that of the known Ha, Ki or N-ras genes and its sequence shows evolutionary conservation, as demonstrated by hybridisation to the genomic DNA of several mammalian species. A pUC19 subclone (pK42), carrying a 1.3kb insert, shows supercoil heterogeneity in plasmid preparations, as does a second compatible plasmid introduced into the same bacterial host with pK42. It appears therefore that the subclone is encoding a product that affects DNA topoisomerase activity in E. coli.

Linkage disequilibrium of plasminogen polymorphisms and assignment of the gene to human chromosome 6q26-6q27

Linkage disequilibrium was observed between newly identified DNA polymorphisms and a previously described protein polymorphism for plasminogen. This finding implies that the two types of polymorphisms describe variation at the same locus. The plasminogen gene was mapped to chromosomal bands 6q26-q27 using somatic-cell hybrids and in situ hybridization. Linkage disequilibrium between protein and DNA polymorphisms has utility in substituting for protein typing in instances where only DNA samples are available, such as from deceased individuals or extinct species. The technique may be useful when cross-hybridizing sequences make the interpretation of Southern blot patterns difficult and may obviate the need for extensive DNA sequencing. In some cases, disequilibrium may provide information useful for determining the appropriate direction for chromosome walks from a marker locus to a target locus.

Efficient isolation of X chromosome-specific single-copy probes from a cosmid library of a human X/hamster hybrid-cell line: mapping of new probes close to the locus for X-linked mental retardation

We isolated X-chromosomal DNA probes from a cosmid library constructed from a single human X/hamster hybrid-cell line (C12D). One hundred human clones were isolated and used to construct a pool of X-chromosomal DNA. This DNA was digested into 0.15-2-kb fragments and subcloned into plasmids allowing the rapid characterization of new single-copy probes. These were regionally mapped and used for the detection of restriction-site polymorphisms. Together with a series of subcloned probes from individually isolated cosmids, we found seven polymorphic probes among 53 tested. Thirty-one of the probes were physically localized to different regions of the X chromosome. Four polymorphic probes map to Xq27-Xq28: DXS102 (cX38.1), DXS105(cX55.7), DXS107(cpX234), and DXS134(cpX67). These were genetically mapped by multipoint analysis relative to previously characterized loci, a mapping that resulted in the following order: DXYS1, DXS107, DXS51/DXS102, F9, DXS105, Fra-X, F8/DXS52, DXS15, DXS134. The mapping of DXS105 between F9 and Fra-X makes this probe useful for Fra-X analysis. For the linkage between FraX and DXS105, a maximum lod score of 5.01 at 4 cMorgans has been obtained in one large Dutch pedigree.

Characterization and use of somatic cell hybrids with interspecific translocations involving the human X chromosome

Two hybrid cell lines, whose only human material was a portion of the X translocated on to a mouse chromosome, have been characterized by cytogenetics, in situ hybridization and Southern blotting. In one hybrid (HORL911R8B) the region Xpter to Xq2(2-4) was identified. In the other (PIP) the single human fragment was found to contain sequences from two separate X chromosomal regions (corresponding approximately to Xp11.4-Xp22.1 and Xq26-Xqter). These two hybrids in combination with a third (WAG 8) retaining Xqter to Xp21 as a human X-autosome translocation chromosome, form a mapping panel for rapid subregional assignments to the human X chromosome. This mapping panel has been used to provide information about the order of DNA sequences derived from the X chromosome and to provide an assignment for an anonymous DNA segment, M201 gamma, to Xp11.4-Xp21.1.

Suppression and re-expression of transformed phenotype in hybrids of HA-ras-1-transformed rat-1 cells and early-passage rat embryonic fibroblasts

Rat-1 cells which had been transformed with the activated Ha-ras-1 gene from human EJ bladder carcinoma cells were fused with diploid embryonic rat fibroblasts. Four selected cell hybrids expressed the human transforming gene product p21 at levels of 10 to 30% compared to 100% in the transformed parental cells. The hybrid cells, however, exhibited normal morphology, anchorage requirement for proliferation, and largely extended latency periods of tumorigenicity in newborn rats. Tumorigenic hybrid derivatives contained lower numbers of chromosomes than the tetraploid parental hybrids. DNA of the non-tumorigenic cell hybrids transformed Rat-1 cells to anchorage-independent proliferation as expected for the transforming human Ha-ras gene present in the donor DNA. We conclude that the transforming properties of the activated Ha-ras gene in Rat-1 cells can be suppressed at the post-translational level by the presence of the genome from diploid embryonic rat fibroblasts but additional controls of expression of the transforming gene are likely to exist. Normal cells contain suppressor gene(s) which safeguard these cells against transformation by the product of the transforming Ha-ras-1 oncogene.

A straightforward approach to isolate DNA sequences with potential linkage to the retinoblastoma locus

From a human-Chinese hamster somatic cell hybrid a clone was derived containing chromosome 13 in duplicate as its only human material. This clone was used to construct a human chromosome 13-specific recombinant DNA-library. Overlapping Sau3AI DNA sequences (11.9-17.2 kb) from the cell hybrid were inserted into the lambda phage vector EMBL4. From eleven recombinants having a human insert thirteen putative unique DNA sequences were isolated and cloned into the plasmid vector pBR329. A human-mouse hybrid containing a human chromosome 13 with a deletion of 13q14 and lacking its undeleted homologue was constructed to be used in a selection procedure for DNA sequences belonging to band q14. Three probes originating from two different phages were assigned to 13q14 because they did not hybridise to DNA from this cell hybrid. One of these 13q14 probes detects a low frequency (2/44) MspI restriction fragment length polymorphism. The probes are now being used for screening a cosmid library to find adjacent polymorphic sequences with a RFLP information content suitable for application in the diagnosis of hereditary retinoblastoma.

Human N-CAM gene: mapping to chromosome 11 by analysis of somatic cell hybrids with mouse and human cDNA probes

We have used mouse and human cDNA probes to map the chromosomal position of the N-CAM gene in the human genome. Southern analysis of DNA isolated from a panel of mouse-human somatic cell hybrids has assigned the N-CAM gene to chromosome 11. This assignment was found with both mouse and human N-CAM cDNAs.

High molecular weight DNA from fixed cytogenetic preparations

Cell pellets that have been stored in routine clinical cytogenetic fixative were studied for the presence of intact DNA. A method for the isolation of high molecular weight DNA from fixed cytogenetic preparations of human leukocytes, bone marrow, and cell hybrid cultures is presented. DNA preparations from fixed pellets were cleaved with restriction enzymes, transferred to nitrocellulose filters after agarose gel electrophoresis, and hybridized to radiolabeled probes to demonstrate that fixed cell pellets could yield DNA of sufficient quality for Southern blot hybridization analysis. This protocol may be useful for molecular analysis of DNA from fixed cell pellets of patients who are unavailable for additional sampling.

Regional localisations and linkage relationships of seven RFLPs and myotonic dystrophy on chromosome 19

We have studied the genetic linkage relationships of seven DNA polymorphisms on chromosome 19, with each other and with the myotonic dystrophy locus. The DNA sequences were localised to various regions of the chromosome using translocations in somatic cell hybrids. These results provide the basis for a linkage map of most of chromosome 19, and suggest that the myotonic dystrophy locus is close to the centromere.

Coordinate control of anchorage independence, actin cytoskeleton, and angiogenesis by human chromosome 1 in hamster-human hybrids

A panel of hybrids previously derived from fusions between a chemically transformed hamster cell line and normal human fibroblasts (A. Stoler and N. Bouck, Proc. Natl. Acad. Sci. USA, 82: 570-574, 1985) has been used to test whether or not anchorage independence, lack of actin cables, and angiogenic activity, three characteristics of transformed cells considered necessary but not sufficient for neoplasia, are coordinately regulated. In these hybrids anchorage independence is initially suppressed and those hybrids where it remains suppressed have been shown to retain human chromosome 1. Here we show that suppressed hybrids also display actin microfilament cables characteristic of normal cells and are unable to elicit an angiogenic response in the rat cornea assay. In contrast, those hybrids in which anchorage independence is expressed and which have lost human chromosome 1 have an actin cytoskeleton resembling that of the transformed parent and are potently angiogenic.

Isolation and characterization of an alpha-satellite repeated sequence from human chromosome 22

We constructed a library in lambda L47.1 with DNA isolated from flow-sorted human chromosome 22. Over 50% of the recombinants contained the same highly repetitive sequence. When this sequence was used to probe Southern blots of EcoRI-digested genomic DNA, a ladder of bands with increments of about 170 bp was observed. This sequence comigrates with satellite III in Ag+/Cs2SO4 gradients and may account for at least part of the 170 bp Hae III ladder seen in isolated satellite III DNA. Partial sequence analysis revealed homology to the 171 bp monomeric repeat unit of alpha-R1-DNA and the X specific alpha-satellite consensus sequence. After low stringency in situ hybridization, silver grains were found over the centromeres of a number of chromosomes. Under high stringency conditions, however, the labeling was concentrated over the centromeric region of chromosome 22. This localization was confirmed using DNA from a panel of human/hamster cell lines which showed that the homologous 2.1 and 2.8 kb EcoR1 restriction fragments were chromosome 22 specific. These clones therefore contain chromosome 22 derived alpha-satellite sequences analogous to other chromosome-specific satellite sequences described previously.

An approach to the study of structure-function relationships of MHC class I molecules: isolation and serologic characterization of H-2Kb somatic cell variants

Somatic cell variants expressing an altered antigenic form of the H-2Kb molecule were isolated for the purpose of performing structure-function analysis of a class I MHC molecule. Over 25 independently isolated variants were derived from an Abelson virus transformed pre- B cell line (R8) by mutagenesis with ethyl methane sulfonate or ethyl nitrosourea. Negative selection was performed by complement-dependent cytotoxicity with anti-H-2Kb monoclonal antibodies subsequently followed by positive selection to separate the H-2Kb surface negative variants from structural variants. Biochemical characterization of a random selection of three independent variants indicated that the variant H-2Kb molecule was present in normal amounts in lysates, and was unchanged in size. Cytofluorometric analysis with the use of a panel of seven monoclonal antibodies against H-2Kb indicated that all of the variants had lost one or more alloantigenic determinants (monoclonal antibody binding sites). For these variants, the pattern of monoclonal antibody loss of recognition suggested that antibody defined alloantigenic determinants appear to be discretely localized to a single domain, either the alpha 1 or the alpha 2 domain, of the H-2Kb molecule. In contrast, CTL recognition of the Kb molecule of these variants depends on involvement of both alpha 1 and alpha 2 domains as shown in the companion paper.

Analysis of somatic cell H-2 variants to define the structural requirements for class I antigen expression

We have taken the approach of producing somatic cell variants with altered H-2 products to study the structural requirements for cell surface expression of class I histocompatibility molecules. H-2 antigen variants generated by chemical mutagenesis of a cell line expressing the H-2b haplotype were first selected with alloantisera for their loss of H-2Kb expression, and then were analyzed by radioimmunoassay for the appearance of intracellular Kb antigen. For one such variant (69.9.15), whereas the H-2Kb antigen was absent from the cell surface as assayed by antibody-mediated complement-dependent cytotoxicity, an H-2Kb molecule was detected within the cell lysate as confirmed by direct immune precipitation with Kb-specific monoclonal antibodies. The product had an altered antigenic phenotype, since it reacted with only two anti-Kb monoclonal antibodies (Y-3 and EH-144) and not with a third (5F1.2). Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis identified the beta 2 microglobulin-associated, intracellular H-2Kb heavy chain to be slightly smaller in Mr than the H-2Kb of the parental cell line. Hybridization analysis revealed the Kb gene from the variant to be without gross alterations, and furthermore, identified a Kb mRNA species that was identical in size to wild-type Kb mRNA. Because complementation was not observed after somatic cell fusion of variant cells with BALB/c splenocytes, it appeared that the alteration in Kb expression was due to a cis-acting defect. In addition, DNA-mediated gene transfer of the wild-type Kb gene into the variant cell line resulted in expression of the Kb antigen on the cell surface, thus confirming that the defect in expression of the mutant Kb product was not due to other factors in the 69.9.15 cell line. Such findings are consistent with the conclusion that stable H-2Kb surface-negative somatic variants can arise due to limited alterations in the Kb gene, resulting in the synthesis of a class I molecule that is expressed only as an intracellular product.

Interleukin 4 (B-cell growth factor II/eosinophil differentiation factor) is a mitogen and differentiation factor for preactivated murine B lymphocytes

Recently we described a murine T-cell hybrid that produces activities that promote the differentiation of eosinophils (eosinophil differentiation factor) and cause proliferation of the BCL1 B-cell lymphoma (B-cell growth factor II activity). Both activities appear to be associated with the same molecule, which has therefore been termed interleukin 4. The hybrid does not produce any other known lymphokines. We now find that purified interleukin 4 has no effects on small resting B cells but induces naturally occurring large B cells (which have presumably been preactivated in vivo) to synthesize DNA and to secrete IgM and low levels of IgG. B cells activated by anti-Ig antibodies apparently only become responsive to the factor once they have reached late G1 stage. All bioactivities of interleukin 4 are associated with a protein of Mr 44,000 (by NaDodSO4/PAGE). Therefore these results demonstrate that this lymphokine alone is sufficient to induce clonal expansion and maturation of activated B cells.

Human chromosome 7 carries the beta 2 interferon gene

A cDNA clone (pAE20-4) corresponding to the 1.3-kilobase human beta 2 interferon mRNA was used as a probe in blot-hybridization experiments of DNA from a panel of human-rodent somatic cell hybrids containing overlapping subsets of human chromosomes. The DNA hybridization experiments showed that the human beta 2 interferon gene is located on human chromosome 7. This assignment is consistent with previous experimental data in which the expression of the translationally active 1.3-kilobase beta 2 interferon mRNA was assayed in various somatic cell hybrids. Blot-hybridization experiments using DNA from different human cell strains and cell lines reveal distinct EcoRI restriction fragment length polymorphisms of the human beta 2 interferon gene.

Characterization of the binding and internalization of tetanus toxin in a neuroblastoma hybrid cell line

Tetanus toxin is known to bind neuronal tissue selectively. To study the interactions of this potent neurotoxin in an intact cell system, the binding of 125I-tetanus toxin was characterized in a neuroblastoma retina hybrid cell line, N18-RE-105. The binding of 125I-tetanus toxin to membranes prepared from N18-RE-105 cells showed many similarities to the interactions of 125I-toxin with rat synaptic membranes. The binding was decreased with increasing temperature, ionic strength, and pH. 125I-Toxin bound to membranes with high affinity: KD = 0.62 +/- 0.05 nM; Bmax = 196 +/- 45 pmol/mg protein. Quantitative thin-layer chromatography and acid-degradation analysis revealed that N18-RE-105 cells contained polysialogangliosides GD1a and GT1b in high concentrations. An assay was developed to quantitate surface-bound and internalized 125I-tetanus toxin by exploiting the observation that surface-bound 125I-toxin is susceptible to pronase digestion. When cells were incubated with 125I-tetanus toxin at 0 degree C, all of the bound 125I-toxin could be degraded with pronase. In contrast, when the incubations were performed at 37 degrees C, within 10 min about 50% of the total cell-associated 125I-toxin was pronase-resistant. Temperature pulse experiments demonstrated that 125I-tetanus toxin that was bound to cells at 0 degree C rapidly disappeared from the surface when the cells were warmed to 37 degrees C, as revealed by the appearance of pronase-resistant radioactivity. This internalization was sensitive to metabolic inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation of antigen-binding membrane molecules from an antigen-specific T-cell hybrid

Cell surface-radioiodinated proteins of a murine T-cell hybrid specific for and able to bind azobenzenearsonate were isolated by adsorption to Sepharose beads conjugated with a rabbit antiserum to murine T-cell antigen-binding molecules. These isolated proteins, Mr 72,000, were found to bind specifically azobenzenearsonate while proteins isolated in this manner from the tumor parent BW5147 did not bind azobenzenearsonate. Similar cell surface proteins were isolated by affinity for antigen and immunoprecipitated with an antiserum to T-cell antigen-binding molecules. The results suggest that antigen-binding T cells express T-cell antigen-binding molecules as membrane receptors for antigen.

Identification of 200,000-dalton human cell surface protein encoded by gene mapped to long arm of chromosome 11

Cell surface proteins and glycoproteins of human and Chinese hamster cells and their hybrid cell clones were analyzed by two-dimensional gel electrophoresis. The J1 clone of human-Chinese hamster hybrid cells contained chromosome 11 as its only human chromosome. The J1 cells expressed a glycoprotein of 200,000 daltons which was shared by human fibroblasts but not by the parental Chinese hamster ovary cells. The 200,000-dalton protein was identified as a cell surface protein by the method of lactoperoxidase-catalyzed iodination. The protein was electrophoretically purified from radioiodinated cultures of human fibroblasts and J1 cells and subjected to the analysis of tryptic peptides by thin-layer electrophoresis followed by chromatography. The protein from both sources gave rise to fingerprints which closely resembled to each other. The results are consistent with a hypothesis that the 200,000-dalton protein of the J1 clone is of human origin. Analysis of segregant clones of J1 cells, which have deletions on human chromosome 11, has further suggested that the gene for this glycoprotein maps to the long arm of chromosome 11. A gene coding for the 200,000-dalton protein has not been previously mapped to this chromosome.

Gene mapping in chicken-Chinese hamster somatic cell hybrids. Serum albumin and phosphoglucomutase-2 structural genes on chicken chromosome 6

Chicken phosphoglucomutase (PGM-2), serum albumin, vitamin D binding protein (Gc) and phosphoribosyl pyrophosphate amidotransferase (PPAT) structural genes have been mapped to chicken chromosome 6 using chicken-Chinese hamster somatic cell hybrids containing this chromosome as the only chicken genetic material. Chicken PGM-2 activity was detected in the hybrids using cellogel electrophoresis and a substrate, ribose-1-phosphate (R-1-P), that allows the detection of PGM-1 activity in mice and PGM-2 activity in humans. Chicken albumin sequences were detected in the hybrids with the use of a labelled chicken serum albumin cloned cDNA. Classical studies have shown linkage of the serum albumin and Gc genes, and the Gc gene also can be localized to chicken chromosome 6. The PPAT gene was localized to this chromosome in previous studies using these hybrids. A homologous linkage group has been identified in mammals and, therefore, a chromosomal linkage group containing at least four genes--Gc, serum albumin, PPAT, and PGM-2--has been conserved over a period of 300 million years, throughout both avian and mammalian evolution.

Fractionation of large mammalian DNA restriction fragments using vertical pulsed-field gradient gel electrophoresis

A new design for pulsed field gradient (PFG) gel electrophoresis of large (greater than 50 kb) DNA fragments is described. The method eliminates distortion of migration of DNA because of the geometry of the applied electric field, requires a single power supply and a simple switching device, and is extremely simple to use. Parameters investigated include variation in pulse time, conditions of restriction enzyme digestion and DNA concentration, and the use of different restriction endonucleases. The method has been applied to restriction enzyme digested mammalian DNA from Chinese hamster and human/Chinese hamster hybrid sources and has allowed examination of the minimum separation of two DNA markers known to be on the same human chromosome, chromosome 21.

A 200 kDa surface glycoprotein of human fibroblasts encoded by a gene on chromosome 11 is regulated by cyclic AMP

A gene mapped to the long arm of human chromosome 11 was previously characterized to code for a cell-surface glycoprotein of an apparent molecular mass of 200 kDa in fibroblasts. We now report that this surface protein is expressed in an increased amount when human fibroblasts or human X Chinese-hamster hybrid cells containing human chromosome 11 are treated with 1 mM dibutyryl cyclic AMP. A detailed analysis of this phenomenon of induction was performed using a long-established, stable cell line of human X Chinese-hamster hybrid cells, J1 clone, which contained human chromosome 11 and expressed the 200 kDa glycoprotein of human origin. It was shown that the 200 kDa protein of J1 cells was inducible with 1 mM dibutyryl cyclic AMP, 10 mM unmodified cyclic AMP, 0.2 mM 8-para-chlorophenylthio cyclic AMP or 1 nM cholera toxin. Induction was potentiated by the addition of a phosphodiesterase inhibitor, Ro 20-1724. These results are consistent with the finding in human fibroblast, confirming that human fibroblasts express a 200 kDa glycoprotein on their surface which is regulated by intracellular concentrations of cyclic AMP. The regulation may be at the level of transcription since the addition of actinomycin D prevented the induction.

Structural and functional features of a cell surface phosphoglycoprotein associated with tumorigenic phenotype in human fibroblast x HeLa cell hybrids

Monoclonal antibodies have been raised against a dimeric cell surface antigen (p75/150) which is specifically associated with the tumorigenic phenotype in human fibroblast X HeLa hybrids. During biosynthesis, a precursor molecule (p70/140), was associated with microsomal membranes in vivo but possessed no detectable cytoplasmic domains. At this stage, each p70 monomer contained 3 "high-mannose" type N-linked glycans which were subsequently processed into endoglycosidase H-insensitive complex oligosaccharides on the mature cell surface forms. Cleavage of this cell surface form with endoglycosidase F yielded non-N-glycosylated polypeptides of Mr = 60,000/120,000. All the monoclonal antibodies identified similar non-N-glycosylated polypeptides in cells grown in the presence of tunicamycin. p75/150 could be weakly labeled with [3H]palmitic or myristic acid. In vivo, p75/150 was found to be phosphorylated on serine residues. Immunoprecipitates of p75/150 from HeLa or tumorigenic hybrid cell lysates exhibited protein kinase activity in vitro, which phosphorylated p75/150 itself, also on serine residues. We were unable to detect this kinase activity in normal fibroblasts and in the nontumorigenic hybrid cells. Furthermore, we were unable to detect p75/150 or its precursors by either cell surface labeling, metabolic labeling, or Western blotting in nontumorigenic cell hybrids; p75/150 thus represents a tumor-specific marker in this system. Tryptic peptides of highly purified p75/150 have been generated, but their amino acid sequences did not reveal any significant homology with previously described proteins.

Chromosome-specific subfamilies within human alphoid repetitive DNA

Nucleotide sequence data of about 20 X 10(3) base-pairs of the human tandemly repeated alphoid DNA are presented. The DNA sequences were determined from 45 clones containing EcoRI fragments of alphoid DNA isolated from total genomic DNA. Thirty of the clones contained a complete 340 base-pair dimer unit of the repeat. The remaining clones contained alphoid DNA with fragment lengths of 311, 296, 232, 170 and 108 base-pairs. The sequences obtained were compared with an average alphoid DNA sequence determined by Wu & Manuelidis (1980). The divergences ranged from 0.6 to 24.6% nucleotide changes for the first monomer and from 0 to 17.8% for the second monomer of the repeat. On the basis of identical nucleotide changes at corresponding positions, the individual repeat units could be shown to belong to one of several distinct subfamilies. The number of nucleotide changes defining a subfamily generally constitutes the majority of nucleotide changes found in a member of that subfamily. From an evaluation of the proportion of the total amount of alphoid DNA, which is represented by the clones studied, it is estimated that the number of subfamilies of this repeat may be equal to or exceed the number of chromosomes. The expected presence of only one or a few distinct subfamilies on individual chromosomes is supported by the study, also presented, of the nucleotide sequence of 17 cloned fragments of alphoid repetitive DNA from chromosome 7. These chromosome-specific repeats all contain the characteristic pattern of 36 common nucleotide changes that defines one of the subfamilies described. A unique restriction endonuclease (NlaIII) cleavage site present in this subfamily may be useful as a genetic marker of this chromosome. A family member of the interspersed Alu repetitive DNA was also isolated and sequenced. This Alu repeat has been inserted into the human alphoid repetitive DNA, in the same way as the insertion of an Alu repeat into the African green monkey alphoid DNA.