Sequencing And Analysis Of Plasmids PC48-1 And PX73 From Avian Strains Of Pasteurella Multocida

In this study, two native plasmids , designated pC48-l and pX73, were isolated and purified from two avain Pasteurella multocida (Pm) strains C48-1 and X73. The whole sequences of pC48-l and pX73 were obtained by using cloning and a primer walking strategy. The complete nucleotide sequences of pC48-l and pX73 are 2 621 bp and 4 220 bp respectively.The G+C contents of pC48-l and pX73 are 41.6% and 42.8% respectively. They are not average in the whole sequences. A number of repeat sequences were found in pC48-l and pX73. Six direct repeats (DR) and six inverted repeats (IR) were found in pC48-1. Six DR and twelve IR were found in pX73. The lengths of all these repeat sequences are longer than 10 bp. Six putative open reading fragments (ORFs) were identified in both strands of pC48-1. However, nineteen ORFs were identified in both strands of pX73. Most of these ORFs are overlapping. There are no codon bias of coding sequences in both ORFs of pC48-1 and pX73. However, the G+C contents of coding sequences are significantly increased in comparison to these of the whole sequences. The G+C contents of coding sequences of pC48-l and pX73 are 49.66% and 46.96% respectively.Nine single restriction endonuclease sites including Acc65 I , BamH I , Bcl I , HindIII, Kpn I, Nhe I, Sea I, Stu I and Xba I were found in pC48-l. Six single restriction endonuclease sites including AceIII, Cla I , Hinc II, M.Hind II, Nhe I and Stu I were found in pX73.Databank searches for homology revealed that the nucleotide sequences of pC48-l and pX73 show high similarities to 15 and 14 known sequences respcetively. Both nucleotide sequences of pC48-l and pX73 show significant similarities to plasmid pLEM from Pm strain P1059. Five of six ORFs of pC48-l show different similarities to known proteins. The ORF2 and ORF4 of pC48-l have complete similarities to a transport protein of pLEM of P1059. Thirteen of nineteen ORFs of pX73 show diverse similarities to known proteins. The ORF7, ORF9, ORF13, ORF14, ORF15, ORF16, ORF17 and ORF18 of pX73 show more than 90% similarities to a mobilization protein A or B of a number of bacteria including Actinobacillus pleuropneumoniae.Thus, by sequencing and analysis of pC48-1 and pX73, the results of the present study provide theoretic basis for constructing gene vector based on plasmid of Pm and will play a...