Identification of the Escherichia coli tonB gene product in minicells containing tonB hybrid plasmids.

Sotlillm clodtq~l sul~~t~e/polyacrylarnide gel :tnwlysis ot’ protrins t~codcd by ii sc>rics ot’ to?/ R + plasmids in minicells has icknt~ified the torLB gene product ws a prokin wit)h km apparent, molecular weight of’ 36,000. A parallel analysis of s(‘vcn tort N mnt,ations which have been genetically crosst~i onto a tonB+ plasmid support,s this itkntification; t)he 36,000 M, protein is tlbsent from t,he scxt, of prot)cins cncotM hy each tonR plssmitl. Four of’ the tonH mlltations arty a,pparently IS1 insrrt.ions. The locatjions of’ thcsr instlrtions within tonf? have I-xten clctermincd by restriction cndont~clcasc mapping. Corrrlnt,ion of’ t,hssc IS 1 insclrtion siks with the molcculwr uxights of’ prt~mat,uroly tc~rminatett torrH polypcptid~s, srrggPst,s that, toaH is tr;mscrihrd in t.hcl direction opposite t,o t,hat of’ the nearby tryptophan opt’ron. In addit,ion, a, prot,ein cxncotlctl hy onr ot’ the invcrtcd rcsl)c;tt s(‘(IIlvnccs of’ tht, t~ranq~osak~lv c~l~nwnl ‘I’n,i ha,s txw> t~cmtativt~l> iclrmtificvl.