DAB1 - A DEGENERATE RETROTRANSPOSON-LIKE ELEMENT FROM NEUROSPORA-CRASSA

A repeated DNA sequence in the genome of Neurospora crassa has been id entified as a family of degenerate retroelements. Retroelements encode protein sequences with clear homology to the reverse transcriptase, R Nase H and endonuclease products of the pol genes common to retrovirus es and retrotransposons. These sequence comparisons place the N. crass a element within the gypsy group of retrotransposons, akin to other el ements found in filamentous fungi. However, the Neurospora element is defective, as no flanking long terminal repeats (LTRs) could be distin guished and the pol gene homologues contain numerous stop codons as a result of multiple base substitutions. The base composition of the ele ment displays significant under-representation of the dinucleotide CpA , the preferred target site of repeat-induced point mutation (RIP). Th e genomic sequences exhibit G:C to A:T transitions between copies whic h are diagnostic of RIP. The degenerate retroelement has accordingly b een designated by the acronym dab-1 (dead and buried).