In general, the compactnes of genomes is a characteristic of
prokaryotes, but there are several eykaryotes that have
overlapping genes: many parasites and endosymbionts. The best
studied of these are the fungal parasites of the phylum
microsporidia and the nucleomorphs (remnant nuclei of algal
endosymbionts in cryptophytes and chlorarachniophytes). cDNA
library was constructed from the microsporidian Antonospora
locustae and 1,146 cDNA clones were sequenced. Here is part of
the expression profile (1): Of the 871 clones found to encode
recognizable genes, 97 transcripts (11%) from 70 distinct loci
encoded sequence from more than one gene (Fig. 1 A ; see also
Table 1, which is published as supporting information on the
PNAS web site). The polyA sites of these clones do not
correspond to polyA tracts in the genome, so they are unlikely
to derive from DNA contamination (see also below), but instead
come from polyA RNA. In prokaryotes, polycistronic mRNAs
commonly code for multiple proteins (11), but with few exce