Disease relevance of pir

• In our present study, we have found that the pi level in cell extracts of Escherichia coli strains containing R6K derivatives is surprisingly high (approximately equal to 10(4) dimers per cell) and that this level is not altered in cells carrying high copy number pir mutants [1].
• Construction of a plasmid containing the pi structural gene (pir) downstream from the inducible pR promoter of bacteriophage lambda provided high levels of production of pi protein in E. coli [2].

High impact information on pir

• Moreover, it was shown that the altered pi protein was not overproduced in maxicells carrying this mutant plasmid and had a higher affinity to the repeated sequence which is present in the pir promoter region [3].
• The mutations were mapped in the pir gene which encodes the pi initiation protein for plasmid R6K DNA replication [3].
• The wild-type and a high copy mutant (Cos405) pir gene were inserted downstream of promoters of different strengths to measure the copy number of an R6K gamma replicon as a function of a 1000-fold range of intracellular pi concentrations [1].
• Plasmid pRK419, a derivative of the naturally occurring antibiotic resistance plasmid R6K, contains the pir gene that codes for the pi initiation protein and the beta and gamma replication origins of R6K [4].
• Nucleotide sequence analysis of the cos405 mutant confirmed the pir gene location of the mutation and showed that this mutation results in a single amino acid substitution (glycine to aspartic acid) at the 81st position of the 305-amino acid pi protein [4].

Chemical compound and disease context of pir

• Transcription in vitro from the pir promoter but not the trp promoter of E. coli, was inhibited by purified pi protein indicating that the pi protein alone is responsible for repression of its own gene and that the effect is promoter specific [5].

Biological context of pir

• This protein binds to two sites in the operator region of the pir gene: a 22-base pair nonpalindromic sequence and a pair of palindromic 9-base pair sequences [6].
• The minimal beta-replicon of plasmid R6K contains an open reading frame for a 151-amino acid protein in addition to the seven 22-base pair direct nucleotide sequence repeats, the structural gene (pir) for the pi initiation protein, and the beta-origin sequence that have been shown to be required for replication activity [7].
• We propose that the interaction of pi protein with the palindromic part of the pir operator is essential for autoregulation; we also propose that there is a fundamental difference in the mechanisms of pi protein recognition of palindromic and nonpalindromic sequences [6].
• The DNA-protein interaction sites in the pir regulatory region have been determined for the pi protein and E. coli RNA polymerase using the DNase I protection method [5].
• Purified mutant pi protein obtained from a temperature-sensitive initiation mutant (pir 105-ts) exhibited temperature-sensitive binding activity to the gamma-origin region, whereas two mutant proteins exhibiting a high copy number phenotype were unaltered (pir104-cop) or slightly reduced (pir1-cop) in binding activity [2].

References