Molecular cloning and characterization of endogenous feline leukemia virus sequences from a cat genomic library

Abstract

Recombinant bacteriophage lambda clones from a cat genomic library derived from placental DNA of a specific pathogen-free cat were screened to identify endogenous feline leukemia virus (FeLV) sequences. Restriction endonuclease mapping of four different clones indicates that there are a number of similarities among them, notably the presence of a 6.0- to 6.4-kilobase pair (kbp) EcoRI hybridizing fragment containing portions of sequences homologous to the gag, pol, env, and long terminal repeat-like elements of the infectious FeLV. The endogenous FeLV sequences isolated are approximately 4 kbp in length and are significantly shorter than the cloned infectious FeLV isolates, which are 8.5 to 8.7 kbp in length. The endogenous elements have 3.3- to 3.6-kbp deletions in the gag-pol region and approximately 0.7- to 1.0-kbp deletions in the env region. These deletions would render them incapable of encoding an infectious virus and may therefore be related to the non-inducibility of FeLV from uninfected cat cells and the subgenomic expression of these endogenous sequences in placental tissue. It appears that there is conservation in the ordering of restriction sites previously reported in the proviruses of the infectious FeLVs in sequences corresponding to the pol and env boundary as well as the region spanning the env gene of the endogenous clones, whereas a greater divergence occurs among restriction sites mapped to the gag and part of the pol regions of the infectious FeLV. Such deleted, FeLV-related subsets of DNA sequences could have originated either by germ-line integration of a complete ecotropic virus followed by deletion, or by integration of a preexisting, defective, deleted variant of the infectious virus.

Defective endogenous proviruses are expressed in feline lymphoid cells: evidence for a role in natural resistance to subgroup B feline leukemia viruses

“…Endogenous feline leukemia virus (FeLV)-related (en-FeLV) sequences are found in the genomes of domestic cats and related small feline species (2,3). enFeLV sequence family members are polymorphic, present at 8 to 12 copies per cell, and arranged as proviruses which generally retain both long terminal repeat (LTR) sequences (42,43). Many of the enFeLV elements contain extensive deletions, while even the apparently full-length enFeLV proviruses appear to be defective; none have yielded infectious virus, and those which have been analyzed in detail have mutations in essential structural genes (27).…”

Molecular analysis of several classes of endogenous feline leukemia virus elements

“…These endogenous sequences are present in multiple copies dispersed throughout the cat genome and are expressed as subgenomic transcripts in a tissue-specific manner (3,24,25,26), but they are not inducible as infectious viral particles (2,28). We previously described the structure of a subset of these endogenous sequences isolated from a recombinant cat genomic library (41). These long terminal repeat (LTR)-flanked sequences were approximately 4 kilobase pairs (kb) long (significantly shorter than the cloned infectious FeLV isolates) and contained 3.3to 3.6-kb deletions in the gag-pol region and 0.7to 1.0-kb deletions in the env regions.…”

Structural analysis of type II variants within the mouse intracisternal A-particle sequence family

“…type II IAP elements is similar (-10%) throughout the element, indicating that AIIins and the flanking type I IAP sequences were probably amplified as a unit. Several endogenous retroviral element families and the copia-like element families include deleted forms (7,38,39) but these have not been…”