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The human enzyme, lysosomal acid phosphatase ACP2, is expressed in nan-rodent somatic cell hybrids as a dimeric molecule. The human-rodent heteropolymer, as well as the human and rodent homopolymer, is associated with lysosomes in these cells. The genes specifying lysosomal acid phosphatase ACP(2) and LDH A are syntenic.

The expression of the adenylate kinase isozymes and of phosphopyruvate hydratase was studied in man-mouse and man-hamster hybrid clones. Concordant segregation of the loci coding for AK-2 and PPH was observed in 54 of 55 primary hybrid clones, and these loci were demonstrated to be synthetic with the loci specifying PGM-1 and PGD. The pattern of expression of the four enzymes in discordant clone suggests the gene order 1pter-(PGD, PPH)-AK-2-PGM-1-centromere. In addition, AK-1 was found to be expressed independently of AK-2.

Two types of alpha-D-mannosidase isozymes are present in human white blood cells, human diploid fibroblasts, and HeLa cells. One of these (the S isozyme) constitutes the major alpha-D-mannosidase of the human cells, has a pH optimum of 4.4, and is associated with lysosomes. The other (the F isozyme) is most active at pH 6, is acid labile, and is located in the soluble portion of the cytoplasm. The expression of human lysosomal alpha-D-mannosidase was examined in man-hamster hybrid clones, and was found to be concordant with that of phosphohexose isomerase in 54 of 55 primary clones. A locus specifying human lysosomal alpha-D-mannosidase has therfore been assigned to chromosome 19.

Human mitochondrial NADP-dependent isocitrate dehydrogenase (IDH-2) is expressed in man-mouse somatic cell hybrids as a dimeric molecule. The gene specifing this enzyme was observed to be syntenic with the mannose phosphate isomerase locus in the 56 primary man-mouse clones in this series. The human IDH-2 locus, therefore, may be assigned to chromosome 15.

The human enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) forms heteropolymers with the rodent enzyme in man-rodent somatic cell hybrids. A gene specifying GAPDH is syntenic with the genes specifying the glycolytic enzymes triosephosphate isomerase (TPI) and lactate dehydrogenase B (LDH-B). The synteny of GAPDH, TPI, and LDH-B is the first evidence for the syntenic association of human genes that specify enzymes of the Embden-Meyerhof glycolytic pathway.

Human Alu repeat ("BLUR") sequences have been cloned into the mini-plasmid vector piVX. The resulting piBLUR clones have been used to rescue selectively, by recombination, bacteriophage carrying human DNA sequences from genomic libraries constructed using DNA from rodent-human somatic cell hybrids. piBLUR clones are able to retrieve human clones from such libraries because at least one Alu family repeat is present on most 15 to 20 kb fragments of human DNA and because of the relative species-specificity of the sequences comprising the Alu family. The rapid, selective plaque purification achieved results in the construction of a collection of recombinant phage carrying diverse human DNA inserts from a specific subset of the human karyotype. Subfragments of two recombinants rescued from a mouse-human somatic cell hybrid containing human chromosomes X, 10, 13, and 22 were mapped to human chromosomes X and 13, respectively, demonstrating the utility of this protocol for the isolation of human chromosome-specific DNA sequences from appropriate somatic cell hybrids.