SUMMARYWe have determined the nucleotide sequence of an almost full-length clone of porcine parvovirus (PPV). The sequence is 4973 nucleotides (nt) long. The 3' end of virion DNA shows a Y-shaped configuration homologous to rodent parvoviruses. The 5' end of virion DNA shows a repetition of 127 nt at the carboxy terminus of the capsid proteins. The overall organization of the PPV genome is similar to those of other autonomous parvoviruses. There are two large open reading frames (ORFs) that almost entirely cover the genome, both located in the same frame of the complementary strand. The left ORF encodes the non-structural protein NS1 and the right ORF encodes the capsid proteins (VP1, VP2 and VP3). Promoter analysis, location of splicing sites and putative amino acid sequences for the viral proteins show a high homology of PPV with feline panleukopenia virus and canine parvoviruses (FPV and CPV) and rodent parvovirus. Therefore we conclude that PPV is related to the Kilham rat virus (KRV) group of autonomous parvoviruses formed by KRV, minute virus of mice, Lu III, H-I, FPV and CPV.

A revised physical map of the alpha-haemolysin plasmid pHly152 has been constructed. The known position of the hly genes in the restriction map of pHly152 allowed us to locate in it a direct repeat of IS elements flanking the hly genes of pHly152. These elements are IS92L, which is a derivative of the previously characterised element IS91 (1.85 kb) by insertion of a sequence of 1.2 kb, and IS92R, an element related to IS91 by a deletion of 0.7 kb and substitution of a 0.2 kb sequence of IS91 by a 1.2 kb heterologous sequence. IS92L is, in turn, flanked by an inverted repetition of sequences of 1.4 kb. These and previously published data strongly suggest that the hly genes spread at some time in evolution by means of the recombinational activity of IS91-like elements.

We determined the DNA sequences surrounding the junctions of IS91 in two insertion derivatives: pSU234 (pACYC184::IS91) and pSU240 (pBR322::IS91). The termini of IS91 consist of two imperfect inverted repeats eight base pairs long. Their sequence is 5'-TCGAGTAGG. . . CCTATCGA-3'. Insertion of IS91 did not generate direct repetitions in the target DNAs.

IS91 is a 1.85 kb insertion sequence originally resident in the alpha-hemolytic plasmid pSU233. The element was transposed sequentially from this plasmid to pACYC184, to R388, and to pBR322. Both cointegrates and simple insertions of the element were obtained. A detailed restriction enzyme map of the element is presented. This does not bear any relationship to the maps of previously described insertion sequences. Furthermore, hybridization between these sequences and IS91 could not be demonstrated. Deletion derivatives of IS91 were constructed which are unable to transpose. However, their transposition can be complemented in trans by wild-type elements. One of these deletion derivatives has been genetically labeled with a kanamycin resistance marker from Tn5. When this new element was complemented for transposition, only about 2% of the transposition products were cointegrates. Thus, the behavior of IS91 is better explained by transposition models that allow direct transposition.

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