Mutants of Escherichia coli with temperature-sensitive lesions in membrane phospholipid synthesis: genetic analysis of glycerol-3-phosphate acyltransferase mutants

Summary Escherichia coli mutants possessing temperature-sensitive lesions in glycerol-3-phosphate acyltransferase, the enzyme catalysing the first step in phospholipid biosynthesis, have been characterized genetically. By recombinational and complementation tests, the mutants have been found to map in a single locus, called plsA, which is cotransducibile with the purE locus and lies between the purE and proC loci at minute 13 on the E. coli genetic map.     

Chemical speciation and health risks of airborne heavy metals around an industrial community in Nigeria

Abstract

Quantification of PM_2.5 (particulate matter <2.5?µm) bound heavy metals and their potential health risks were carried out around a cement manufacturing company in Ewekoro, Nigeria. The PM_2.5 samples were collected using Environtech gravimetric sampler. A four-staged sequential extraction procedure was used to fractionate PM_2.5 bound chromium (Cr), lead (Pb), aluminum (Al), copper (Cu), and silver (Ag), and further analyzed using inductively coupled plasma mass spectrometry. Chemical speciation results reveal bioavailable levels of Pb (4.05?µg/m³), Cr (10.75?µg/m³), Al (16.47?µg/m³), Cu (4.38E-01?µg/m³), and Ag (1.22E-02?µg/m³) in the airborne particulates. Pb and Cr levels exceeded the World Health Organization allowable limit of 0.5 and 2.5E-05?µg/m³, respectively. The labile phases showed strong indication of the presence of Cr and Cu metal. Excess cancer risks exposure for adults, outdoor workers and children were higher than the acceptable risk target level of 1E-06. Non-carcinogenic health risk estimated using hazard quotients (HQs) and hazard indices (HIs) showed ingestion route within the safe level of HI <1 implying no adverse effect while inhalation route exceeded the safe level for all receptors. Enforcement of pollution control by authorized agencies, and screening of greenbelts as sinks for air pollutants is strongly recommended.     

Isolation and Characterization of an Escherichia coli K-12 Mutant with a Temperature-Sensitive RecA− Phenotype

A mutation that causes a temperature-sensitive RecA(-) phenotype was identified in a derivative of a PolA(-) strain that failed to grow at high temperature. The mutant allele (recA200) was shown to be linked to cysC, conferred a sharply temperature-sensitive, ultraviolet-sensitive Rec(-) phenotype in the range 35 to 42 C, and in crosses failed to show complementation at 42 C with Hfr's that transferred recA(-). Double mutants that carried both recA200 and polA were examined for ability to grow and synthesize DNA at restrictive temperatures.     

Distinct functional contributions of three potential secondary structures in the phage G4 origin of complementary DNA strand synthesis

Three potential secondary structures, stem-loops I, II, and III, are contained in the phage G4 origin of complementary DNA strand synthesis, G4oric, and are believed to be involved in its recognition by dnaG-encoded primase and the synthesis of primer RNA. In a previous publication [Sakai et al., Gene 71 (1988) 323-330], we suggested that base pairing between the loops of stem-loops I, and II, and/or II and III, might play a role in G4oric function. To test this hypothesis, site-directed mutagenesis was used to construct mutants which carried base substitutions in loops I, II and III that destroyed possible interloop base pairing. These mutations, however, did not seriously affect G4oric activity. This indicates that base pairing between the loops is not essential for G4oric functional activity, and also that base substitutions which do not affect the secondary structure of stem-loops I, II and III, do not affect G4oric activity. To complete an analysis of the effects of altering the structure of the G4oric stem-loops, insertions were made into stem-loop III. In contrast to stem-loops I and II, all insertions into stem-loop III destroyed in vivo G4oric activity.