Import of proteins into chloroplasts depends on an N-terminal transit sequence. Transit sequences contain little primary sequence similarity and therefore recognition of these sequences is thought to involve specific folding. To assess the conformational flexibility of the transit sequence, we studied the transit peptide of preferredoxin (trfd) by circular dichroism. In buffer, trfd is in a random coil conformation. A large increase in ~-helix was induced in the presence of micelles or vesicles formed by anionic lipids. Less pronounced changes in secondary structure were induced by zwitterionic detergents but no changes were observed in the presence of neutral detergents or vesicles composed of phosphatidylcholine.
The ‘main’ phase transition Lβ→Lα of hydrated 1,2‐dipalmitoylphosphatidylethanolamine (DPPE) bilayers in excess water affects the ESR order parameter S
33 of N‐cetyl‐N,N‐dimethyl‐N‐tempoylammonium bromide (CAT‐16), 5‐doxylstearic acid (5‐DSA) and 16‐doxylstearic acid (16‐DSA) spin probes. The ‘pretransition’ and ‘subtransition’ suggested to occur in hydrated DPPE by Chowdhry et al. [(1984) Biophys. J. 45, 901–904] and Silvius et al. [(1986) Biochemistry 25, 4249–4258], respectively, affect exclusively the S
33 of CAT‐16, but not that of 5‐DSA and 16‐DSA spin probes. The subtransition occurs about 15 ± 1°C below the main transition.
Plasmid-curing activity of N,N'-bis(decyldimethyl)-1,6-hexanediammonium dibromide, BDHD, was tested on six different plasmids in E. coli and plasmid pKM 101 in S. typhimurium. BDHD eliminated the F'lac plasmid from E. coli cells only with a low efficiency. Plasmid pKM 101 was eliminated from S. typhimurium cells significantly and this effect was dependent on an outer membrane pattern. A deep-rough mutant of S. typhimurium is completely resistant to curing activity of BDHD, while part-rough and smooth cells are susceptible to it. In contrast to pKM 101, a cryptic plasmid being present in S. typhimurium cells was not eliminated by BDHD. The curing activity of sodium dodecyl sulfate, acridine orange, crystal violet, and promethazine was also affected by the outer membrane pattern of S. typhimurium cells.
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