(1) The amino acid sequence deduced from the DNA sequence was determined for the plasmid-coded and the ScrY porin coded in the chromosome of Klebsiella pneumoniae.
(2) Primer extension analysis and site-directed mutagenesis were used to identify the precise location of the promoter of scrY, scrA, and scrB.
(3) This increase in sucrose permeability provided strong evidence that the ScrY protein functions as a sucrose porin.
(4) A putative cyclic AMP receptor protein binding site centered 72.5 bp upstream of the start point of transcription of scrY appeared to be essential for full activity of the scrY promoter.
(5) Furthermore, the presence of ScrY restored growth on maltodextrins in cells devoid of LamB, thus complementing the lack of this maltoporin.
(6) Reconstitution experiments with lipid bilayer membrane demonstrated that ScrY formed ion-permeable channels with properties very similar to those of general diffusion pores of enteric bacteria.
(7) This sounds shocking, but dig a little deeper and some of this soul-scrying voodoo becomes slightly less terrifying.
(8) The binding of different sugars to ScrY and LamB of E. coli is discussed with respect to the kinetics of sugar movement through the channel.
(9) A frameshift mutation in the scrY gene resulted in a dramatic decrease in sucrose transport with no effect on in vitro phosphorylation activity associated with enzyme IISer.
(10) There was 23% amino acid sequence identity between the ScrY protein and LamB, a maltose porin from Escherichia coli.
(11) One of the different gene products of the plasmid is the outer membrane protein, ScrY.
(12) During the molecular analysis of a plasmid-coded sucrose metabolic pathway of enteric bacteria, a gene, scrY, was found whose product, ScrY, had all the properties of a bacterial porin (Schmid et al., 1988).
(13) In ScrR+ cells, readthrough transcription from the putative scrK promoter into scrY accounted for less than 10% of scrY expression.
(14) The scrY gene, part of the pUR400-borne sucrose regulon, appeared to be transcribed from its own promoter, with the transcriptional start site located 58 bp upstream from the initiation codon.
(15) The four genes form an scr operon (gene order, scrK scrY scrA scrB, transcription from K to B), regulated by a repressor (gene scrR, 37 kD) and inducible by sucrose, fructose and fructose-containing oligosaccharides.
(16) Gene scrK apparently codes for an intracellular and ATP-dependent fructokinase (39 kD), while scrY seems to code for a sucrose porin (58 kD) in the outer cell membrane.
(17) The rate of diffusion of sucrose was 96 times greater than the rate of diffusion of lactose or maltose in liposomes containing the ScrY protein.