Tom is a retrovirus described in Drosophila ananassae (Tanda et al. 1988). Tom is expressed in the nurse cells during oogenesis, in the central and peripheral nervous systems during embryonic development, and also, in the imaginal discs of the larvae. Tom is mobilized with high frequency in the female germinal lines of the "ca;px" strain (Tanda, Mullor and Corces 1994), and its insertion results in mutations inducing dominant phenotypes in eyes. This specificity may be explained by the Tom-induced-over-expression of the homeotic gene Om (1D) at the eye imaginal discs of third-instar larvae (Tanda et al. 1988; Tanda and Corces 1991; Tanda, Mullor and Corces 1994). Tom belongs to the genus Errantiviridae (Boeke et al. 1999; Pringle 1998; 1999; Hull 1999), a lineage of fly-retroviruses and LTR retrotransposons phylogenetically related to 412/mdg1 clade (Tubio, Naveira and Costas 2005). The genomic structure of Tom is 7 Kb in size including LTRs of 474 nt. The internal region displays a Primer Binding Site (PBS) complementary to a tRNASer, three Open Reading Frames (ORFs) for gag, pol, and env genes, and a Polypurine Tract (PPT) adjacent to the 3´LTR (Tanda, Mullor and Corces 1994).
Figure not to scale. If present, long terminal repeats (LTRs) have been highlighted in blue. Amino acid motifs noted with lines indicate the conserved residues in each protein domain, abbreviations below mean:
||DU or DUT=dUTPase
||TAV or IBMP=transactivator/viroplasmin or inclusion body matrix protein
||PBS=primer binding site
||ATF=aphid transmission factor
||VAP=virion associated protein