A second gene for type I signal peptidase in Bradyrhizobium japonicum, sipF, is located near genes involved in RNA processing and cell division.
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.
Bairl
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A
FB Biologie/Molekulare Zellbiologie und Angewandte Botanik, Philipps Universität Marburg, Germany.
Müller
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P
D000595:Amino Acid Sequence; D020369:Bradyrhizobium / Q000201:enzymology / Q000235:genetics*; D002455:Cell Division / Q000235:genetics; D003001:Cloning, Molecular; D004722:Endoribonucleases / Q000235:genetics; D018628:Gene Dosage; D015870:Gene Expression; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D009876:Operon; D012323:RNA Processing, Post-Transcriptional / Q000235:genetics; D011993:Recombinant Fusion Proteins; D015183:Restriction Mapping; D043244:Ribonuclease III; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D012697:Serine Endopeptidases / Q000235:genetics*
D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; D004722:Endoribonucleases; D043244:Ribonuclease III; D012697:Serine Endopeptidases; C026515:type I signal peptidase