ABSTRACT
Spontaneous quinolone-resistant mutants obtained from Salmonella typhimurium Su694 were screened for mutations by direct DNA sequencing of an amplified PCR gyrA fragment. Substitutions Ser-83-->Phe (Ser83Phe), Ser83Tyr, Asp87Tyr, and Asp87Asn and double mutation Ala67Pro-Gly81Ser, which resulted in decreased sensitivities to ciprofloxacin, enoxacin, pefloxacin, norfloxacin, ofloxacin, and nalidixic acid, were found. The levels of resistance to quinolones for each mutant were determined.
Subject(s)
Anti-Infective Agents/pharmacology , DNA Topoisomerases, Type II/genetics , Mutation , Salmonella typhimurium/drug effects , Salmonella typhimurium/genetics , Amino Acid Sequence , Base Sequence , DNA Gyrase , DNA, Bacterial/genetics , Drug Resistance, Microbial , Fluoroquinolones , Molecular Sequence Data , Polymerase Chain Reaction , Sequence Homology, Amino Acid , Sequence Homology, Nucleic AcidABSTRACT
Autographa californica nuclear polyhedrosis virus-specific RNA synthesis in isolated nuclei of Spodoptera frugiperda cells in culture was monitored at different times postinfection. Up to 8 h postinfection viral RNA synthesis remained sensitive to 5 mug of alpha-amanitin per ml. During the course of infection this sensitivity decreased, and at 24 h postinfection RNA synthesis was completely resistant to alpha-amanitin. DEAE-Sephadex profiles of RNA polymerase isolated at 24 h postinfection showed a new, chromatographically distinct, alpha-amanitin-resistant form whose kinetics and response to divalent cations differed from those of the host RNA polymerases. The possibility that this enzyme may be responsible for viral late transcription is discussed.
ABSTRACT
A new type-II restriction endonuclease SphI, has been partially purified from Streptomyces phaeochromogenes. SphI recognizes the hexanucleotide sequence 5'-GCATGC and cleaves it at the position marked by the arrow. This nucleotide sequence is present twice in SV40 DNA, four times lambda DNA and only once in the cloning vehicles pBR322, pBR325, pBR327 and pBR328.
