Isolation and characterization of the ATP-binding cassette (ABC) transporter system genes from loofah witches' broom phytoplasma

Abstract

A clone containing a 3903 bp EcoRI-restriction fragment was obtained from a λ_ZAP genomic library of loofah witches' broom (LfWB) phytoplasma by plaque hybridization using a PCR fragment as a probe. Sequence analysis revealed that this fragment contained three open reading frames (ORFs). The deduced amino acid sequences of ORF 1 and ORF 2 showed a high homology with the ATP-binding proteins of the ABC transporter system genes of prokaryotes and eukaryotes, and encoded proteins with a molecular mass of 36 and 30 kDa, respectively. Based on amino acid sequence similarity, secondary structure, hydrophilicity and a signal peptide sequence at the N-terminus, we predicted that ORF 3 might encode a specific solute-binding prolipoprotein of the ABC transporter system with a molecular mass of 62 kDa. The cleavage site of this prolipoprotein signal peptide was similar to those of gram-positive bacteria. In addition to nutrient uptake, ABC transporter systems of bacteria also play a role in signal transduction, drug-resistance and perhaps virulence. The possible implications of the system to the survival and the pathogenesis of phytoplasma were discussed.

• Loofah witches' broom (LfWB)
• phytoplasma
• ATP-binding cassette (ABC) transporter system
• open reading frames

• AF086618 (P36)
• AF086619 (P30)
• AF086620 (P62)

Acknowledgements

We thank Dr Te-Chang Lee, Researcher of the Institute of Biomedical Sciences, Academia Sinica, Taiwan for providing aid in DNA autosequencing. Thanks also go to Dr Michael Conrad of University of North Carolina at Chapel Hill for his critical reading and suggestions. This work was financially supported by the National Science Council, Taiwan to K.-C. Ho (Grant No. NSC93-2621-B-002-011).