EVIDENCE FOR POST TRANSCRIPTIONAL REGULATION OF THE SYNTHESIS OF THE ESCHERICHIA-COLI HLYB HEMOLYSIN TRANSLOCATOR AND PRODUCTION OF POLYCLONAL ANTI-HLYB ANTIBODY
Ma. Blight et al., EVIDENCE FOR POST TRANSCRIPTIONAL REGULATION OF THE SYNTHESIS OF THE ESCHERICHIA-COLI HLYB HEMOLYSIN TRANSLOCATOR AND PRODUCTION OF POLYCLONAL ANTI-HLYB ANTIBODY, MGG. Molecular & general genetics, 247(1), 1995, pp. 73-85
Extensive attempts were made to overexpress the Escherichia coli haemo
lysin translocator protein HlyB, and HlyB fragments, utilising high co
py number plasmids or hlyB expressed from strong promoters including l
ambda pR ptrp and the T7 promoter. Analysis of both cytoplasmic and me
mbrane fractions failed to detect any overexpression of the protein, a
lthough all the constructs showed biological activity and there was no
evidence of HlyB-induced toxicity. In some constructs, the effect of
removing a stem-loop structure, immediately upstream of the start codo
n and implicated in rho-independent termination of transcription, was
tested but this did not lead to overexpression. Nevertheless, analysis
of hlyB specific mRNA synthesis revealed that some constructs showed
at least a 50-fold increase in mRNA levels, indicating that expression
of HlyB may be limited at the translational level. When HlyB was expr
essed as a hybrid, downstream of LacZ, extremely high level overproduc
tion was then detected in total cell extracts. When the expression of
HlyB or HlyB fragments expressed from a T7 promoter was examined, the
C-terminal ATPase domain was dramatically overexpressed but the produc
tion of fragments encompassing the N-terminal membrane domain, was red
uced at least 1000-fold. These results indicate that mRNA structures c
orresponding to the membrane domain of HlyB greatly limit the post-tra
nscriptional expression of HlyB. When such structures are deleted, or
disrupted when part of a larger mRNA, HlyB or the HlyB ATPase domain c
an be overproduced in milligram quantities and this has facilitated th
e production of high titre antibodies to HlyB.