The DNA sequence and minimal replicon of the Corynebacterium ghtamicum plasmid pSRl : evidence of a common ancestry with plasmids from C .

1753 The DNA sequence and minimal replicon of the Corynebacterium ghtamicum plasmid pSRl : evidence of a common ancestry with plasmids from C. diphtheriae The complete nucleotide sequence of pSR1, a 3 kb multicopy cryptic plasmid from Curynebacterium ghtamicum ATCC 19223 has been determined. pSRl is unrelated to the 4.4 kb Brevibacterium lactofermenturn plasmid pBLl and shows no DNA sequence conservation with plasmids from Staphylococcus. Transposon insertion and deletion mutants located the minimal replicon to within a 2.1 kb NcoI-BclI restriction fragment. This region contains a single large open rea4ng frame, ORF2, flanked at the 5' end by a series of inverted repeat sequences which may modulate its expression, and at the 3 end by a region which may contain a replication origin. ORF2 (position 163S2636) with a maximum coding potential of 36 kDa is essential for pSRl replication and was designated the rep gene. The predicted ORF2 protein product exhibits 47% identity over a length of 343 amino acids with a replication-associated O W in the C. diphtheriae plasmid pNG2, many of the changes being in the third base position. This observation suggests that pSRl and pNG2, which are two plasmids from environmentally separated Corynebacterium species, may share a common ancestral rep gene.