Abstract
The TnphoA-induced Bradyrhizobium japonicum mutant 184 shows slow growth and aberrant colonization of soybean nodules. Using a DNA fragment adjacent to the transposon insertion site as a probe, a 3.4-kb BglII fragment of B. japonicum 110spc4 DNA was identified and cloned. Sequence analysis indicated that two truncated ORFs and three complete ORFs were encoded on this fragment. A database search revealed homologies to several other prokaryotic proteins: PdxJ (an enzyme involved in vitamin B6 biosynthesis), AcpS (acyl carrier protein synthase), Lep or Sip (prokaryotic type I signal peptidase), RNase III (an endoribonuclease which processes double-stranded rRNA precursors and mRNA) and Era (a GTP-binding protein required for cell division). The mutation in strain 184 was found to lie within the signal peptidase gene, which was designated sipF. Therefore, sipF is located in a region that encodes gene products involved in posttranscriptional and posttranslational processing processes. By complementation of the lep ts E. coli mutant strain IT41 it was demonstrated that sipF indeed encodes a functional signal peptidase, and genetic complementation of B. japonicum mutant 184 by a 2.8-kb SalI fragment indicated that sipF is expressed from a promoter located directly upstream of sipF. Using a non-polar kanamycin resistance cassette, a specific sipF – mutant was constructed which exhibited defects in symbiosis similar to those of the original mutant 184.
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Received: 10 July 1998 / Accepted: 3 August 1998
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Bairl, A., Müller, P. A second gene for Type I signal peptidase in Bradyrhizobium japonicum, sipF, is located near genes involved in RNA processing and cell division. Mol Gen Genet 260, 346–356 (1998). https://doi.org/10.1007/PL00008631
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DOI: https://doi.org/10.1007/PL00008631