Low-level inversion of the L component of pseudorabies virus is not dependent on sequence homology.
Pseudorabies virus has a class 2 genome in which the S component is found in two orientations relative to the L component. The L component is bracketed by sequences that are partially homologous; it is found mainly in one orientation, but a small proportion is inverted (J. M. DeMarchi, Z. Lu, G. Rall, S. Kuperschmidt, and T. Ben-Porat, J. Virol. 64:4968-4977, 1990). We have ascertained the role of the patchy homologous sequences bracketing the L component in its inversion. A viral mutant, vYa, from which the sequences at the right end of the L component were deleted was constructed. Despite the absence of homologous sequences bracketing the L component in vYa, its L component inverted to an extent similar to that of the L component in the wild-type virus. These results show the following. (i) The low-frequency inversion of the L component of PrV is not mediated by homologous sequences bracketing this component. (ii) Cleavage of concatemeric DNA at the internal junction between the S and L components is responsible for the appearance of the minority of genomes with an inverted L component in populations of pseudorabies virus. (iii) The signals present near or at the end of the S component are sufficient to allow low-frequency cleavage of concatemeric DNA; the sequences at the end of the L component are not essential for cleavage, although they enhance it considerably.
Rall
G F
GF
Department of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
Kupershmidt
S
S
Lu
X Q
XQ
Mettenleiter
T C
TC
Ben-Porat
T
T
D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D007446:Chromosome Inversion; D004279:DNA, Viral / Q000235:genetics; D016679:Genome, Viral; D011558:Herpesvirus 1, Suid / Q000235:genetics*; D008969:Molecular Sequence Data; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid; D014162:Transfection; D014771:Virion / Q000235:genetics
D004279:DNA, Viral