Davis RE, Dally EL, Jomantiene R, Zhao Y, Roe B, Lin S, and Shao J. 2005. Cryptic plasmid pSKU146 from the wall-less plant pathogen Spiroplasma kunkelii encodes an adhesin and components of a type IV translocation-related conjugation system. PLASMID 53:179-190.
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Physical and genetic map of plasmid pSK146 from Spiroplasma kunkelii strain CR2-3X. Putative protein-coding regions (open reading frames, ORFs) and direction of transcription are represented by open arrows. palSK1, 58 bp palindromic sequence. IRSK, inverted repeat units potentially forming a hairpin structure. Putative oriTA and oriTB regions are indicated by broken arrows. Cleavage sites of selected restriction endonucleases are indicated.
A cryptic plasmid of the wall-less plant pathogenic mollicute, Spiroplasma kunkelii CR2-3X, was cloned and its sequence analyzed. The 14,615 bp plasmid, designated pSKU146, has a nucleotide content of 28 mol% G+C, and contains 18 potential protein coding regions (open reading frames, ORFs), of which six encode proteins that exhibit similarity to virulence-associated proteins involved in cell-to-cell adhesion or conjugal DNA transfer. One ORF encodes a 96 kDa protein, SkARP1, that is highly similar to SARP1 adhesin involved in attachment of S. citri to insect vector gut membrane. Five ORFs encode proteins similar to TraE and Mob in walled bacteria, and to ORFs found in the integrative, conjugative element (ICEF) of Mycoplasma fermentens, respectively. Presence of domains similar to proteins of the Type IV secretion system in pathogenic bacteria suggests that spiroplasma possesses a related secretion system. Plasmid pSKU146 also contains two identical oriT regions each containing a nick sequence characteristic of the IncP conjugative plasmid family, as well as a 58 bp palindromic sequence, palSK1. Features in pSKU146 suggest that the plasmid functions as a mobile genetic element in conjugative transmission of spiroplasma pathogenicity-related genes.