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The human leukemia cell line K562, derived from a patient with Philadelphia chromosome-positive chronic myelogenous leukemia, contains amplified c-abl oncogenes and unrearranged C lambda genes. Using in situ hybridization techniques, we have determined that the amplified c-abl and C lambda DNA sequences of K562 cells are both located on the same abnormal acrocentric marker chromosome, which may represent an altered Philadelphia chromosome.

A human c-erbA oncogene homologue is closely proximal to the chromosome 17 breakpoint in acute promyelocytic leukemia (somatic cell Contributed by Peter C. Nowell, April 5, 1984 ABSTRACT A human cDNA library was screened for sequences homologous to the erbA gene of avian erythroblastosis virus (AEV). One such clone, cHerbA-1, was used to map the chromosomal location of highly homologous human sequences that were found to be present on chromosome 17 as judged by Southern blot screening of a panel of mouse-human hybrid cell lines segregating human chromosomes. cHerbA-1 was hybridized in situ to metaphase chromosomes from a normal male subject and from a female patient with an acute promyelocytic leukemia (APL) having the typical t(15;17) translocation. The results localized the cellular c-erbA sequences on chromosome 17 to the q21-q24 region of normal chromosomes and indicated that the c-erbA sequences remained on the 17q-chromosome in the APL cells, suggesting that they could be assigned to the 17(q21-q22) region. For additional data, we hybridized human neoplastic cells derived from a poorly differentiated acute leukemia carrying a t(17;21) translocation with thymidine kinase (TK)-deficient LMTK-mouse cells. A resulting hybrid, containing only the 21q+ chromosome, did not have human c-erbA sequences. Since the breakpoint on 17q in this translocation was similar to that in the APL t(15;17) translocation, this supported the assignment of c-erbA to the q21-q22 region of chromosome 17. The apparent close proximity of the c-erbA sequences to the chromosomal breakpoints in these two leukemias suggests a possible role for this oncogene homologue in the development of these neoplasms.

Diploid human fibroblasts (IMR-90 cells), grown to confluency and growtharrested by serum starvation, were irradiated with a variety of doses of UV light (0.02540 Jim') or incubated with broad dose ranges of four direct-acting mutagens [ethyl methanesulfonate (EMS), ICR-170, methyl methanesulfonate (MMS), and 4-nitroquinoline oxide (4-NQO)] and pulsed with a thymidine analog, 5-bromodeoxyuridine (BrdUrd) to detect evidence of DNA repair. These cells and appropriate controls were immunochemically stained and subjected to flow cytometric analysis to quantify BrdUrd incorporation into DNA and simultaneously measure cellular DNA content. Since the maximal quantity of BrdUrd incorporated with repairing cells is profoundly less than the amount incorporated during replicative synthesis and flow cytometric analysis collects information on a cell-to-cell basis, data collection using linear histograms succeeded both in revealing repairing cellular populations and eliminating replicative cells from the analysis. Technical modifications necessary to achieve stoichiometry with UV-irradiated IMR-90 fibroblasts included a 48h repair (and pulse) period, followed by denaturing cellular DNA for 15 min at 90°C. The limit of detection was equal to or below the lowest dose investigated (0.025 J/m'). DNA repair was also detected with cultures incubated with low doses of all chemicals and pulsed with BrdUrd for a 24 h period. The limits of detection were near or below 500 pM EMS, 5 pM MMS, 0.25 pM 4-NQO, and 0.1 pM ICR-170. o 1993 Wiley-Liss, Inc.Key terms: Ethyl methanesulfonate, flow cytometry; EMS; ICR-170; IMR-90 cells; methyl methanesulfonate, MMS; 4-nitroquinoline oxide, 4-NQO; unscheduled DNA synthesis, UDS Mammalian cells possess a variety of mechanisms for restoring the integrity of DNA damaged by environmental or endogenous agents. Some instances of damage are repaired with minimal disturbance to the DNA molecule (ex. photoreactivation of UV-induced cyclobutane pyrimidine dimers by a dimer-specific endonuclease), whereas other repair processes, exemplified by several types of excision repair, remove not only the lesion, but excavate a considerable number of adjacent nucleotides in the process (26). With this latter circumstance, DNA integrity is restored by resynthesizing the excised domain and ligating this patch to the parental DNA strand. Various analytical methods have been developed to detect and quantify DNA excision repair in cells, typified by assays that measure 'Abbreviations: BrdUrd, 5-Bromodeoxyuridine; BU, BrdUrd con-

The canine metaphase karyotype consists of 78 chromosomes. All autosomes exhibit telocentric or acrocentric configurations gradually diminishing in size. These features make identification of homologous pairs by conventional analysis difficult.Chromosome preparations were derived from short-term cultures of peripheral blood lymphocytes obtained from clinically normal dogs representing at least four breeds. Most components of the canine karyotype can be distinguished readily. No significant G-banding pattern variations were detected in the individuals screened. An idiogrammatic interpretation of the banding pattern is presented. Apart from bands, other characteristic morphologic features were found which aid in identification. The G-banding pattern of the canine metacentric X is quite similar to that of the banded human X. The canine Y is a minute metacentric having two positive bands.