Escherichia coli protein signal sequences

The gene for this protein has also been isolated from A. faecalis and sequenced and expressed in Escherichia coli cells (Yamamoto et al., 1987). Like azurin, it contains an amino-terminal signal sequence, suggesting that it is secreted into the periplasm in A. faecalis, although not all of the blue protein is found in this fraction. Mutants of this protein are being made and characterized in T. Beppu s laboratory (Univ. of Tokyo) (personal communication, 1989). 

Promoter region of the nar operon, which encodes nitrate reductase in Escherichia coli. The promoter is generally only maximally induced under anaerobic conditions. It has been shown that the nar promoter in some strains of Escherichia coli can be induced under conditions of very low oxygen tension in the presence of nitrate. This observation has been used to develop some useful processes for recombinant protein expression in Escherichia coli. See Li, S.F. and DeMoss, J.A., Promoter region of the nar operon of Escherichia coli nucleotide sequence and transcription initiation signals, J. Bacteriol. 169, 4614- 620, 1987 Han, S.J., Chang,... 

Archaea contain a stable 7S RNA species of unknown function, which is not associated with the ribosome. The 7S RNA gene from Halobacterium halobium NRC817 has been cloned and sequenced [120]. The sequence resembles the 7SL RNA of eucarya [85] and the 4.5S Escherichia coli) or sc Bacillus subtilis) RNAs of bacteria [121] in potential secondary structure. The 7SL RNA forms part of the signal-recognition particle, involved in protein translocation. The function of the 4.5S RNA is not known exactly, but it is known to be essential [122]. 

The removal of the signal sequence which directs the transport of secreted proteins is a critical step in protein export. Extensive studies by Randall, Hardy and coworkers have demonstrated that the leader sequence prevents the proper folding of the mature polypeptide within the cytoplasm (55,54). For the E.coli 6-lactamase, the presence of the leader sequence decelerates the folding kinetics but does not prevent the formation of the enzymatically active conformation (55). Bowden and Georgiou (56) showed that the mode of translocation of 6-lactamase across the cytoplasmic membrane of Escherichia coli exerts a profound effect on the folding of the mature protein following secretion, presumably by affecting the unfolded state in the periplasmic space. 

Utsumi, S. C.S. Kim T. Sato M. Kito. Signal sequence of preproglycinin affects production of the expressed protein in Escherichia coli. Gene 1988, 71, 349-358. 

Incubations with Cloned, Expressed Enzymes Individual UGT enzymes have been expressed in a wide variety of systems including insect cells (Supersomes or Baculosomes), Escherichia coli, yeast, and mammalian cells. Zakim and Dannenberg have demonstrated that the lipid membrane composition can influence activity (Zakim, 1992). There tends to be excellent protein expression insect cells transfected with baculovirus, but when activity is measured compared to mammalian cells systems, there appears to be significant amounts of inactive protein due to either poor membrane insertion or improper folding (lack of chaperones ). Bacteria do not have an ER, but alteration of the signal sequence results in active membrane bound preparations. Yeast and mammalian cells such as HEK293 or V79 cells have a more typical membrane environment and may be preferable for expression of ER proteins. 

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