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Adsorption protein of filamentous bacteriophage variant phiXo from Xanthomonas oryzae

Liu, T.J.; You, B.Y.; Tseng, T.T.; Lin, N.T.; Yang, M.T.; Tseng, Y.H.

Botanical Bulletin of Academia Sinica 42(3): 193-199

2001


Accession: 010133653

variant phiXo, Xf, variant phiLf, variant phiXv, and Cf are filamentous bacteriophages isolated in Taiwan. Both variant phiXo and Xf specifically infect Xanthomonas oryzae pv. oryzae, and variant phiLf, variant phiXv, and Cf specifically infect X. campestris pv. campestris, X. campestris pv. vesicatoria, and X. campestris pv. citri, respectively. In this study, the variant phiXo gene III (gIII) encoding the adsorption protein (pIII) was cloned by probing with the variant phiLf gIII. Sequence analysis revealed that the variant phiXo gIII is 1,023-nt long and able to encode a pre-protein of 340 aa (35,337 Da), with structural features typical of filamentous phage adsorption proteins: an N-terminal signal sequence (18 aa), a central region (90 aa) containing 38 glycine, 29 aspartic acid and 19 histidine residues, and a C-terminal membrane-anchoring domain (17 aa). The variant phiXo pIII purified from the phage particles migrated as a 42-kDa band in SDS-polyacrylamide gel, which is substantially larger than that deduced from the nucleotide sequence, presumably due to the presence of the long stretch of charged residues in the central region. The variant phiXo pIII could cross-react with the antiserum specific to variant phiLf pIII, which also cross-reacts with variant phiXv pIII. Like the situations in variant phiLf and variant phiXv, the pIIIs of variant phiLf and variant phiXo are also interchangeable. The gIII and the flanking regions of variant phiLf, variant phiXv and variant phiXo are highly homologous and similar in size, but variant phiXo has a genome (7.6 kb) larger than that of variant phiLf (6.0 kb) and variant phiXv (6.4 kb), suggesting that variant phiXo is able to accommodate more genes and/or have longer intergenic regions in the remaining part of the genome. Difference in sizes between the pIIIs indicates that variant phiXo and Xf, which has a predicted pre-pIII of 488 aa (51,036 Da), are distinct phages.

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