Transposon Tn10-dependent expression of the lamB gene in Escherichia coli

Abstract

Among TnlO insertions isolated in or near the malB region of Escherichia coli, one (zjb-729::TnlO) mapped between malK and lamB or late in malK and allowed MalT-independent expression of lamB. TnlO-dependent expression of a lamB-lacZ protein fusion was 25% of the expression of the fusion from the malK-lamB operon promoter in maiTh constitutive strains. The maltoporin content of a strain carrying this TnlO was about 20% that of a maiTh malB+ strain. Transport of maltose at concentrations of below 10-6 M was reduced about threefold. When maltoporin was present at about 50% of the level of mal7 malB+ strains, maltose transport was largely restored. We conclude that maltoporin is not rate limiting for maltose transport in wild-type cells but becomes rate limiting when the ratio of maltoporin to other maltose transport components is reduced more than twofold.

The LysR‐like regulator LeuO in Escherichia coli is involved in the translational regulation of rpoS by affecting the expression of the small regulatory DsrA‐RNA

“…This is because of the presence of the relatively strong p out promoter in the IS10 elements, which gives rise to an antisense transcript that regulates the expression of Tn10 transposase (Halling et al, 1982;Simons et al, 1983). When Tn10 is appropriately inserted, p out can produce a stable transcript that may also contain the message for downstream chromosomal genes (Ciampi et al, 1982;Simons et al, 1983;Brass et al, 1984). Therefore, the localization of Tn10-8 just 26 bp upstream of leuO with the putative ribosomal-binding site (Shine-Dalgarno sequence) fully intact suggested that the phenotypes of the Tn10-8 insertion mutant could be caused by overproduction of LeuO protein instead of its elimination.…”

Genetic evidence for substrate and periplasmic-binding-protein recognition by the MalF and MalG proteins, cytoplasmic membrane components of the Escherichia coli maltose transport system

“…we replaced the malB region in these strains with the malB region from a strain (HS3140) that is AmalE444 malF+ malG+ malK+ lamB+ and has a TnWO transposon (zib-729::TnJO) closely linked to the malB genes (5). This was done by transducing 15 Mal+ revertants to Tcr with a P1 lysate grown on HS3140.…”

Maltose-binding protein does not modulate the activity of maltoporin as a general porin in Escherichia coli

“…1. The malE254 mutation confers P1 of JB55-29; select Tcr, screen Mal-P1 of JB56-29 into JB105; select Tcr, screen Mal+ P1 of MM407 (lamB102 zjb-729::TnIO) P1 of SH205 (zah-735::TnlO AlacUI69) into Tcs isolates of JB104 through JB106 (still contain P10 of ;jb-729::TrlIO [9]) P1 of JB55-42; select Tcr, screen Mal+ P1 of JB55-42; select Tcr, screen Mal-P1 of JB56-42 into JB103; select Tc', screen Mal-…”

“…1). zjb-729::TnlO allows TnJO-dependent constitutive expression of lamB at a level that is 25% of the wild-type level (9). This low level of expression of lamB was an advantage for this study, since lactose permeation through the outer membrane is the rate-limiting step up to fairly high lactose concentrations (0.2 mM) for the overall uptake process in strains carrying zjb-729::TnJO (see below).…”

“…The malE gene codes for MBP, lamB codes for maltoporin, and malF,G,K code for cytoplasmic membrane components of the maltose transport system (14,30). Transposon zjb-729: :TnJO is located between malK and lamB and allows malT-independent transcription of lamB at 25% of the level in malB+ cells from a TnlO promoter (P10) (9).…”