title: Structural and functional analysis of pCI65st, a 6.5 kb plasmid from Streptococcus thermophilus NDI-6.
abstract: The 6.5 kb cryptic plasmid pCI65st from Streptococcus thermophilus NDI-6, a strain isolated from the Indian fermented milk dahi, was subcloned and sequenced. Five putative ORFs were identified. ORF1 could encode a 315 aa polypeptide almost identical to the RepA protein of previously sequenced S. thermophilus plasmids, indicating that pCI65st is one of the pC194 group of small gram-positive rolling-circle plasmids. ORFs 2 and 4 were virtually identical and could specify proteins of approximately 150 aa with significant similarity to the small heat-shock proteins described from a variety of gram-positive bacteria. ORF3 could encode a 415 aa protein similar to enolase, an enzyme involved in glycolysis and gluconeogenesis. ORF5 could encode a 412 aa protein which had high similarity to the HsdS (specificity) proteins of type I restriction-modification systems. Variants of strain NDI-6 which lacked pCI65st were readily isolated after subculture of the parent strain at 32 degrees C. The plasmid-bearing parent culture was significantly more resistant to a temperature shift from 42 degrees C to 62 degrees C than its plasmid-free variant and expressed proteins which corresponded with the predicted translation products from ORF2 and ORF4. In addition, plasmid-free mutants were lysed in broth by bacteriophages to which the parent culture was resistant.
authors: Tadhg
authors: T
authors: O'Sullivan
authors: Douwe
authors: D
authors: van Sinderen
authors: Gerald
authors: G
authors: Fitzgerald
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics; D001433:Bacteriolysis; D003001:Cloning, Molecular; D004265:DNA Helicases; D015280:DNA Restriction-Modification Enzymes / Q000737:chemistry / Q000235:genetics; D004268:DNA-Binding Proteins; D004591:Electrophoresis, Polyacrylamide Gel; D005798:Genes, Bacterial / Q000235:genetics; D014644:Genetic Variation / Q000235:genetics; D006094:Gram-Positive Bacteria / Q000235:genetics; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018869:Heat-Shock Response; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016366:Open Reading Frames / Q000235:genetics; D010751:Phosphopyruvate Hydratase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010957:Plasmids / Q000235:genetics* / Q000502:physiology; D011506:Proteins / Q000737:chemistry / Q000235:genetics; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013291:Streptococcus / Q000201:enzymology / Q000235:genetics* / Q000502:physiology / Q000821:virology; D017108:Streptococcus Phages / Q000502:physiology; D015534:Trans-Activators
chemical_list: D001426:Bacterial Proteins; D015280:DNA Restriction-Modification Enzymes; D004268:DNA-Binding Proteins; C113046:HSDS protein, Bacteria; D006360:Heat-Shock Proteins; D011506:Proteins; D015534:Trans-Activators; C045264:replication initiator protein; D004265:DNA Helicases; D010751:Phosphopyruvate Hydratase