A genetic system comprised of mammalian cell mutants which demonstrate concomitant resistance to a number of unrelated drugs has been described previously. The resistance is due to reduced cell membrane permeability and is correlated with the presence of large amounts of a plasma membrane glycoprotein termed P-glycoprotein. This system could represent a model for multiple drug resistance which develops in cancer patients treated with chemotherapeutic drugs. We demonstrate here that the multiple drug resistance phenotype can be transferred to mouse cells with DNA from a drug-resistant mutant and then amplified quantitatively by culture in media containing increasing concentrations of drug. The amount of Pglycoprotein was correlated directly with the degree of drug resistance in the transformants and amplified transformants. In addition, the drug resistance and expression of P-glycoprotein of the transformants were unstable and associated quantitatively with the number of double minute chromosomes. We suggest that the gene for multiple drug resistance and P-glycoprotein is contained in these extrachromosomal particles and is amplified by increases in double minute chromosome number. The potential use of this system for manipulation of mammalian genes in general is discussed.A genetic system of clinical relevance involving mammalian cell mutants resistant to a wide variety of cytocidal drugs has recently emerged (36). This system began with the isolation of a number of CHO cell mutants which were resistant to colchicine (38). These mutants were shown to be resistant to the drug as a result of a membrane permeability barrier, which reduced the cellular uptake of colchicine (38). They were also found to be cross-resistant to a number of structurally diverse and functionally unrelated drugs, some of which are used in chemotherapy of cancer, again, by virtue of reduced uptake of these compounds (10). Further analysis of the membranes of these cells, in conjunction with hybrid cell studies (37) and selection of revertants (35), clearly demonstrated the association of the multiple drug resistance phenotype and the reduced membrane permeability with the presence in the cell membrane of a glycoprotein of 160,000 to 180,000 daltons termed P-glycoprotein (27, 28). P-glycoprotein was undetectable in the membrane of the drug-sensitive parental CHO cells but present in drugresistant mutants in amounts directly correlated with the level of resistance. The overexpression of a 160,000-to 180,000-dalton protein has also been observed in several drug resistance systems where resistance has been selected for drugs other than colchicine (13,22,45), including a human leukemic cell line selected for vinblastine resistance (11). As it appears likely that the development of resistance to chemotherapy of human tumors after repeated treatment with these drugs involves, at least in part, the emergence of such mutants (10, 36, 52), it seems important to carry their genetic analysis further. As a first step in this direction, we * Correspondin...

We describe a new method of gene cloning by complementation of mutant alleles which obviates the need for construction of a gene library in a plasmid vector in vitro and its amplification in Escherichia coli. The method involves simultaneous transformation of mutant strains of the fungus Aspergillus nidulans with (i) fragmented chromosomal DNA from a donor species and (ii) DNA of a plasmid without a selectable marker gene, but with a fungal origin of DNA replication ('helper plasmid'). Transformant colonies appear as the result of the joining of chromosomal DNA fragments carrying the wild-type copies of the mutant allele with the helper plasmid. Joining may occur either by ligation (if the helper plasmid is in linear form) or recombination (if it is cccDNA). This event occurs with high efficiency in vivo, and generates an autonomously replicating plasmid cointegrate. Transformants containing Penicillium chrysogenum genomic DNA complementing A. nidulans niaD, nirA and argB mutations have been obtained. While some of these cointegrates were evidently rearranged or consisted only of unaltered replicating plasmid, in other cases plasmids could be recovered into E. coli and were subsequently shown to contain the selected gene. The utility of this "instant gene bank" technique is demonstrated here by the molecular cloning of the P. canescens trpC gene.

An important goal for database systems today is to provide elastic scale-out, i.e., the ability to grow and shrink processing capacity on demand, with varying load. Database systems are difficult to scale since they are stateful -they manage a large database, and it is important when scaling to multiple server machines to provide mechanisms so that these machines can collaboratively manage the database and maintain its consistency. Database partitioning is often used to solve this problem, with each server machine being responsible for one partition. In this paper, we propose that the flexibility provided by a partitioned, shared nothing parallel database system can be exploited to provide elastic scale-out. The idea is to start with a small number of server machines that manage all partitions, and to elastically scale out by dynamically adding new server machines and redistributing database partitions among these servers. We present an implementation of this approach for elastic scale-out using VoltDB -an in-memory, partitioned, shared nothing parallel database system. Our main goal in this paper is to identify several manageability problems that arise when using this approach for elastic scale-out. The paper presents some of these problems and outlines a research agenda for this area.

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When acute supposed ear infections fail to respond to treatment (antibiotics or surgery), rarer causes of the symptoms should be considered. By reporting this case series, we aim to improve the early diagnosis of granulomatosis with polyangiitis to enable timely treatment and prevent systemic involvement.