Downloaded from www.microbiologyresearch.org by IP: 54.157.13.203 On: Tue, 09 Feb 2016 18:05:06 Journal of General Virology (1995), 76, 729-740. Printed in Great Brita& 729 A set of African swine fever virus tandem repeats shares similarities with SAR-like sequences F. Almazfin, J. R. Murgnia, J. M. Rodriguez, I. de la Vega and E. Vifiuela* Centro de Biologia Molecular "Severo Ochoa' ( CSIC-UAM ), Facultad de Ciencias, Universidad Autrnoma, Cantoblanco, 28049 Madrid, Spain A group of cross-hybridizing DNA segments contained within the EcoRI restriction fragments U', X and J of a Vero cell-adapted strain (BA71V) of African swine fever virus (ASFV) were mapped and sequenced. Analysis of the nucleotide sequence revealed the presence of a set of long internal repeated sequences composed of five types of tandemly repeat units of about 200 bp. These tandem repeats contain a G-rich core of 10-14 nucleotides surrounded by regions with a high A+T content distributed in oligo(dA), oligo(dT) tracts. Next to the repeated sequences we detected two related open reading frames that are members of a new multigene family (multigene family 300). Comparison of DNA sequences from several virus isolates indicated that this region undergoes frequent rearrangements leading to either duplications or deletions of the repeat units. These ASFV repeated sequences share similarities with chromosomal ~ satellite DNA, the scaffold-associated region and satellite III of Drosophila. Similar tandemly repeated sequences have not been described in other viruses. Introduction African swine fever virus (ASFV), a large enveloped icosahedral deoxyvirus, is the causative agent of an important disease of domestic pigs and related species of the Suidae family (reviewed in Vifiuela, 1987; Costa, 1990). Unfortunately, although a number of strategies have been explored including immunization with inacti- vated virus particles, inoculation with attenuated ASFV strains and immunization with different purified virus polypeptides, reliable protection against ASFV has never been achieved (Wardley et al., 1987; Escribano et al., 1993). The difficulties encountered in the search for an ASFV vaccine along with the proficiency of the virus to establish persistent infections have led to speculation that ASFV might use mechanisms to counteract the host immune defences. The ASFV genome is a single molecule of double- stranded DNA of approximately 170 kb, with covalently linked ends (Ortin et al., 1979) and terminal inverted repetitions (TIR) (Sogo et al., 1984; de la Vega et al., 1994) similar to those of poxviruses (Wittek & Moss, * Author for correspondence. Fax + 34 1 3974799. e-mail FALMAZAN@MVAX.CBM.UAM.ES The nucleotide sequence data reported have been deposited in GenBank under accessionnumber U13763, 1980; Baroudy et al., 1982). Crosslinks are composed of partially unpaired and A-T-rich sequences that are found as flip-flop forms at the DNA ends (Gonzfilez et al., 1986). Also in common with the poxviruses (Moss, 1990), ASFV particles contain the enzymic machinery required for the synthesis of mature virus early mRNAs (Kuznar et al., 1980; Salas et al., 1981, 1986). Two types of internal repetitions have been described within the genome of ASFV: long (over 200 bp) repeats associated with multigene families located next to the TIR at both ends of the virus genome; and short (10-50bp) repeats detected in both intergenic and intragenic regions. So far, four multigene families have been described and analysed in detail. Multigene families 110 (Almendral et al., 1990), 360 (Gonz~ilez et al., 1990) and 505 (Rodr~guez et al., 1994) were initially detected in the BA71V strain of ASFV; multigene family 100 was first identified in the virulent strain Malawi LIL20/1 (Vydelingum et al., 1993). Genetic variation in ASFV DNA takes place mainly through deletion or addition of DNA sequences in regions located close to the genome ends (Dixon & Wilkinson, 1988; Blasco et al., 1989a). The main variation detected when comparing different virus field isolates is a change in the number of genes belonging to multigene families. Additionally, new genes can be generated by recombination events between homologous genes (Blasco et al., 1989 b; de la Vega et al., 1990; Dixon et al., 1993). Nothing is known about the 0001-2858 © 1995SGM