A timetable for the initiation of DNA replication in human lymphocyte chromosomes has been established by a technique which allows detection of areas of chromosomes replicating at a given interval of the S-phase. The resolution of the method, using 33258 Hoechst-Giemsa staining, is more refined than that obtained with 3H-thymidine autoradiography. Early replicating regions coincide with R-bands. The timetable is rather coarse since replication may start asynchronously in the same region of homologous autosomes of the same metaphase and since even the sequence of bands appearing on individual chromosomes sometimes deviates from the rule.
Using a mouse cDNA probe for ornithine decarboxylase (ODC), we have identified and isolated an ODC cDNA clone from a λ gt11 recombinant library prepared from human liver cell mRNA. The 2.0-kb insert of this clone hybridizes with several mouse genomic ODC DNA restriction fragments under conditions of low stringency, but reacts with only few human DNA fragments and a polyA+ RNA species of 2.2 kb under both nonstringent and stringent hybridization conditions. This suggests that, unlike the mouse genome, there are only few ODC genes in the human genome. The human ODC DNA fragments segregate with chromosome regions 2pter→p23 and 7cen→qter in mouse × human somatic cell hybrid clones containing normal, translocated, and deleted human chromosomes. Sequences of the short arm of chromosome 2 containing the NMYC oncogene at 2p23→p24 are often involved in DNA amplification in neuroblastomas and small-cell lung cancers. However, in at least three cases—one neuroblastoma cell line, one neuroblastoma tumor, and one lung carcinoma—the ODC sequences are not coamplified with the NMYC oncogene.
We report the chromosomal localization of the cellular oncogene SKI, the putative oncogene of the Sloan-Kettering viruses (SKVs), a group of transforming retro viruses that had been isolated from chicken embryo cells infected with the avian leukosis virus tdB77. Southern blot analysis of DNA from mouse × human somatic cell hybrids with the v-SKI probe established synteny with chromosome 1 but excluding the region 1pter→q21. In situ hybridization of the same probe both to human spermatocyte pachytene and lymphocyte metaphase chromosomes enabled precise localization of the gene to the region 1q22→q24, a region that frequently is involved in translocations and other rearrangements in diverse human tumor types. In situ hybridization studies of metaphase spreads from a small noncleaved cell lymphoma that exhibited a t(1; 14)(q21 ;q32) translocation showed that SKI translocates to the der(14) chromosome. Cytogenetic analysis of 65 prospectively ascertained non-Hodgkin’s lymphomas revealed that the SKI region undergoes nonrandom breakage leading to translocations. Further analysis of the chromosome breaks in this group of lymphomas suggested that those involving the SKI site probably are of importance in tumor progression.
A cDNA for a new catalytic subunit (Cγ) of the cAMP-dependent protein kinase (PKA) was recently isolated from a human testis cDNA library. This subunit was shown to be expressed only in testis, and has so far not been demonstrated in other species. In the present study, we have determined the chromosomal localization of this gene employing a cDNA for Cγ as a probe. Southern blot analysis of genomic DNA from human × mouse somatic cell hybrids allowed us to assign this gene (PRKACG) to human chromosome 9. In situ hybridization to metaphase chromosomes confirmed the somatic cell hybrid data and regionally mapped the Cγ gene of PKA to human chromosome 9q13.
Pregnancy specific beta-1-glycoprotein (PSBG), a major product of the human placenta, is encoded by multiple genes. Southern blot hybridization of human × rodent somatic cell hybrid DNAs with a cDNA specific for one member of the PSBG gene family allowed us to map this gene to human chromosome 19. Further analysis using hybrids with subchromosomal segments of 19q revealed that the gene maps to the distal segment of region 19q 13.1.
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