pT3.2I, the smallest plasmid of Thiobacillus T3.2

The whole nucleotide sequence of pT3.2I, the smallest plasmid of the acidop hilic bacterium Thiobacillus T3.2, has been determined. pT3.2I is 15,390 bp long with a 53.7% GC content; Different regions can be defined in it: one 2569-bp putative insertion sequence similar to other insertion sequences of some Agrobacterium Ti plasmids; and a longer sequence, which occurs in two almost identical copies, differing only in a I-bp deletion (6406 and 6405 bp). Several open reading frames and some smaller sequences were found in t his duplicated region: ORFA and ORFG, encoding a putative polyol dehydrogen ase and a putative RepA replication protein, respectively, an 83-bp sequenc e which could code for an antisense RNA, and a 36-bp region highly homologo us to ori sequences of ColE2- and ColE3-related plasmids. Another putative gene, ORFH, is only present in the longer copy of this region (it is delete d in the short copy) and might encode a 90-amino-acid polypeptide which cou ld act as a second replication protein, RepB. Based on sequence comparisons , pT3.2I can be related to plasmids in the pColE2-CA42 incB incompatibility group. (C) 2000 Academic Press.