Genetic Alteration in Animal Cells in Culture

Characterization of a ts mutant of BALB/3T3 cells and correction of the defect by in vitro addition of extracts from wild-type cells.

“…Comparatively little is known about DNA replication in mammalian cells. Despite the availability of mammalian DNA ts mutants (12), they have not been used for in vitro studies with complementation assays of the type that have been so successful in procaryotic systems. The DNA ts mutants that have been isolated and partially characterized have been divided into two groups: those whose defect prevents the cells from entering S phase, and those whose defect directly affects the replication process (2).…”

Genetic Separation of Purine Transport from Phosphoribosyltransferase Activity in Salmonella typhimurium

“…While genetic and biochemical studies (Gots et al, 1972;Hochstadt-Ozer & Stadtman, 1971 b; Roy-Burman & Visser, 1975) have distinguished three PRTs in enteric bacteria (guanine-xanthine, hypoxanthine and adenine PRT) this paper presents the first genetic evidence of a specific purine transport system. Specific transport of guanine was first described by Thakar & Kalle (1968).…”

“…The transport of exogenous purine bases into microbial cells has been described as a group translocation mediated by membrane-bound phosphoribosyltransferases (PRTs) (Berlin & Oliver, 1975;Hochstadt-Ozer & Stadtman, 1971 a ;Jackman & Hochstadt, 1976) during which each base is converted to its corresponding ribonucleotide by 5-phosphoribosyl transfer from 5-phosphoribosyl-1-pyrophosphate. Evidence supporting this conclusion includes the observation that variations in substrates and inhibitors produced similar effects on transport and PRT activity (Zylka & Plagemann, 1975), and that the loss of a PRT activity was always followed by specific defects in purine uptake (HochstadtOzer & Stadtman, 1971 a, b).…”

Uptake to adenosine in a marine bacterium is not an active transport process

“…The uptake experiments were performed in membrane vesicles [5,7,8] or in cells starved up to 48 h at 4°C [6]. In such cells, and in vesicles, membrane integrity and hence the transport properties were probably altered since the membrane became permeable to d ' -5phos-phoribosyl-I-pyrophosphate and to AMP [7].…”

“…In such cells, and in vesicles, membrane integrity and hence the transport properties were probably altered since the membrane became permeable to d ' -5phos-phoribosyl-I-pyrophosphate and to AMP [7]. Moreover, the information obtained from the purification procedure and properties of the phosphoribosyltransferase [4,5] was not sufficient to assume the tr~smembran~ orientation of this enzyme. The group translocation hypothesis was disputed by a number of investigators who suggested that all nucleoside and base interconversion enzymes reside within the cell [9,13] and that transport occurs prior to metabolism [9-141.…”